Preparation method and application of MoP-C electrocatalyst based on polymolybdic acid-based metal organic framework

Abstract

The invention relates to a preparation method and application of a MoP-C electrocatalyst based on a polymolybdic acid-based metal organic framework, and belongs to the technical field of electrocatalytic materials, the preparation method of the MoP-C electrocatalyst comprises the following steps: S1, synthesis of an organic ligand btpe, S2, synthesis of a polymolybdic acid-based metal organic framework CUST-698 crystal, S3, in-situ synthesis of the MoP-C electrocatalyst, and S4, in-situ synthesis of the MoP-C electrocatalyst. The MoP-coated C electrocatalyst is applied to an electrocatalytic hydrogen evolution electrode, the MoP-coated C electrocatalyst or the electrocatalytic hydrogen evolution electrode applying the MoP-coated C electrocatalyst is applied to hydrogen evolution reaction (HER) in acidic or alkaline electrolyte, N2 adsorption and desorption tests prove that the MoP-coated C electrocatalyst has a multi-stage pore channel system composed of micropores and mesopores, and the MoP-coated C electrocatalyst has the advantages that the MoP-coated C electrocatalyst can be applied to the hydrogen evolution reaction (HER) in the acidic or alkaline electrolyte; the MoP-C electrocatalyst prepared by the preparation method disclosed by the invention is favorable for permeation of electrolyte and desorption of hydrogen bubbles, exposes a large number of active sites, has high hydrogen evolution activity, shows SEM and TEM images, effectively prevents agglomeration due to the structure of the MoP-C electrocatalyst, ensures full utilization of the active sites and rapid substance transport, and has good stability.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, and in particular relates to a method for preparing MoP@C electrocatalysts based on polymolybdate metal-organic frameworks and their applications. Background Technology

[0002] Hydrogen energy, due to its high energy density and pollution-free combustion products, is considered one of the most promising clean energy sources. Utilizing electricity to decompose water to produce hydrogen (i.e., the electrocatalytic hydrogen evolution reaction, HER) is a key technology for achieving large-scale green hydrogen production. The core of this technology lies in developing efficient and stable electrocatalysts to reduce reaction overpotential and improve energy conversion efficiency.

[0003] Currently, platinum (Pt) and its alloys are recognized as the best-performing electrocatalysts for hydrogen ether electrolysis (HER), exhibiting near-zero overpotentials and extremely low Tafel slopes in both acidic and alkaline media. However, the scarcity and high cost of platinum severely limit its application in large-scale industrial water electrolysis for hydrogen production. Therefore, the development of alternative catalysts based on non-precious metals that possess both high activity and high stability has become a research hotspot and urgent need in this field.

[0004] In recent years, transition metal phosphides (TMPs), especially molybdenum phosphide (MoP), have attracted widespread attention in the field of electrocatalytic hydrogen evolution due to their platinum-like electronic structure, excellent electrical conductivity, and good chemical stability. In MoP, phosphorus atoms optimize the adsorption free energy of reaction intermediates (such as H*) by modulating the d-electronic state of molybdenum, thereby exhibiting intrinsic electrocatalytic activity.

[0005] However, bulk or pure MoP catalysts still face a series of serious challenges in practical applications: (1) Aggregation problem: During synthesis and reaction, MoP nanoparticles have high surface energy and tend to aggregate and grow, resulting in a sharp decrease in the active specific surface area and a reduction in the number of effective active sites.

[0006] (2) Poor conductivity: Although MoP itself has metallic conductivity, the contact resistance between nanoparticles is large, and it often needs to be mixed with insulating binders in actual electrode preparation. This hinders the rapid transport of electrons in the overall structure of the catalyst and limits the reaction kinetics.

[0007] (3) Insufficient structural stability: In the strong acid or strong alkaline HER working environment, MoP nanoparticles may corrode, dissolve or undergo phase transformation under long-term operation, leading to a decrease in catalytic activity. In addition, the electronic interaction between the carbon support and the active site of catalysts prepared by traditional methods is often weak, lacking in-depth surface chemical state analysis (such as XPS) to confirm their synergistic catalytic mechanism, and the true nature of the active site (such as the specific existence form of Co) is often unclear, resulting in a vague structure-activity relationship and difficulty in targeted optimization.

[0008] To overcome these limitations, researchers commonly employ a strategy of carbon material composites. Loading MoP nanoparticles onto high specific surface area carbon supports (such as carbon nanotubes, graphene, and porous carbon) can effectively suppress particle aggregation, improve conductivity, and enhance structural stability. However, traditional physical mixing or impregnation-calcination methods struggle to achieve uniform and fine dispersion of MoP nanoparticles in a carbon matrix, and the weak interaction between the precursor and the carbon support makes it easy for the active components to sinter or detach from the support during heat treatment.

[0009] Metal-organic frameworks (MOFs) are a class of crystalline porous materials formed by the self-assembly of metal ions / clusters and organic ligands. They possess tunable structures, large specific surface areas, and diverse compositions. In recent years, using MOFs as precursors or templates to prepare metal compound / carbon composites via a one-step pyrolysis method has become an effective strategy. This method enables atomic-level dispersion and confined growth of metal species in a carbon matrix, resulting in uniform sizes.

[0010] Although existing technologies have recognized the potential of MoP and the importance of carbon composites, developing a method for preparing MoP-based catalysts that can achieve highly dispersed active components, excellent conductive network structure, and strong synergistic effects among the components remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for preparing a MoP@C electrocatalyst with highly dispersed active components, excellent conductive network structure, and strong synergistic effect among the components.

[0012] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A method for preparing a MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework includes the following steps: S1. Synthesis of the organic ligand BTPE Under an inert gas atmosphere, 1,2,4-triazole was pre-reacted with a strong base in a polar aprotic solvent (such as dimethyl sulfoxide, DMSO) at 70°C–90°C for 30–60 minutes to generate 1,2,4-triazole salt. Subsequently, a solution of 1,5-dibromopentane was slowly added dropwise to the reaction system, and the reaction was continuously stirred at 75°C–85°C for 8–12 hours. After the reaction was complete, the mixture was cooled to room temperature, and deionized water was added to precipitate the product. The product was then purified by multiple extractions using an organic solvent (such as n-butanol). The organic phases were combined, and the solvent was removed by rotary evaporation to obtain a pale yellow viscous liquid product, btpe ligand.

[0013] S2. Synthesis of polymolybdate-based metal-organic framework CUST-698 crystals Sodium molybdate (Na₂MoO₄·2H₂O), cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O), and the btpe ligand prepared in step S1 were accurately weighed and dissolved in a mixed solution of deionized water and concentrated nitric acid. The amount of concentrated nitric acid added was to adjust the pH of the reaction system to 3.0–4.5 to form stable polymolybdate anion clusters. The mixed solution was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and crystallized at 130–150°C for 72 hours using a hydrothermal method. After the reaction, the mixture was cooled to room temperature, and the resulting pink blocky crystals were collected by centrifugation or filtration. The crystals were washed repeatedly with deionized water and ethanol, and then vacuum dried at 60–80°C to obtain high-purity CUST-698 crystal particles with the molecular formula C. 23 H 30 CoMo5N 16 O 17 .

[0014] In-situ synthesis of S3.MoP@C electrocatalyst a. Preparation of the precursor solution: The CUST-698 crystal particles obtained in step S2 were ground into powder and then dispersed together with phytic acid (PA) in deionized water at a mass ratio of 1:10 to 1:14. The mixture was stirred vigorously at room temperature for 30 to 60 minutes. During this process, the phosphate groups in the phytic acid molecules interact strongly with the metal sites in the CUST-698 crystal framework to form a uniform orange-red pre-assembled complex.

[0015] Preferably, the mass ratio of CUST-698 crystal powder to phytic acid (PA) is 1:12.

[0016] b. Introduction of carbon source: Polyvinylpyrrolidone (i.e., carbon source, PVP, molecular weight approximately 40,000) is dissolved in deionized water and added dropwise to the suspension prepared in step a above. Stirring continues for 6 to 10 hours to ensure that PVP molecules are fully coated on the surface of the pre-assembled composite. The mass ratio of polyvinylpyrrolidone to CUST-698 crystal powder in step S3a above is 0.8:1 to 1.2:1.

[0017] Preferably, the mass ratio of polyvinylpyrrolidone to CUST-698 crystalline powder is 1:1.

[0018] c. Drying and Pyrolysis: Transfer the mixture obtained in step b to a crucible, first evaporate most of the moisture at 80℃~100℃, then thoroughly dry it in a vacuum drying oven at 60℃~80℃ to obtain a fluffy solid precursor. Place this solid precursor in a tube furnace, and under an inert protective atmosphere (such as high-purity nitrogen or argon), program the temperature to the target temperature, i.e., the sintering temperature (800℃~950℃), at a heating rate of 2℃ / min~10℃ / min, and maintain the temperature for 1 hour~3 hours for phosphating / carburizing reaction. After the reaction is complete, allow it to cool naturally to room temperature to obtain the black final product—MoP@C electrocatalyst.

[0019] Preferably, the target temperature is 900°C.

[0020] The MoP@C electrocatalyst is used in the electrocatalytic hydrogen evolution electrode.

[0021] The MoP@C electrocatalyst or the electrocatalytic hydrogen evolution electrode using the MoP@C electrocatalyst is used in the hydrogen evolution reaction (HER) in acidic or alkaline electrolytes.

[0022] Through the above design scheme, the present invention can bring the following beneficial effects: (1) High specific surface area and hierarchical pore structure: N2 adsorption-desorption tests confirmed that the MoP@C electrocatalyst has a BET specific surface area of ​​up to 277 m² / g and a hierarchical pore system composed of micropores and mesopores. This is beneficial for electrolyte permeation and hydrogen bubble desorption, and exposes a large number of active sites, i.e., it has high hydrogen evolution activity.

[0023] (2) Optimized microstructure and dispersibility: SEM and TEM images show that the MoP@C electrocatalyst exhibits a three-dimensional network structure composed of interwoven ultrathin carbon nanosheets. The ultrafine MoP nanoparticles are confined in the carbon matrix, which effectively prevents agglomeration, ensures full utilization of active sites and rapid mass transport, and thus has good stability. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: Figure 1 The following graphs show the LSV curves, Tafel slopes, CV curves, and other parameters of the MoP@C electrocatalyst prepared in Example 3 of this invention and the electrocatalyst obtained in the comparative example in 0.5 M H₂SO₄: (a) LSV curves; (b) Tafel slopes; (c) CV curves; (d) C dl (e) Nyqusit plot; (f) Stability test plot.

[0025] Figure 2 The following figures show the LSV curves (a) and Tafel slope (b) of the MoP@C electrocatalyst prepared in Example 3 of this invention and the electrocatalyst obtained in the comparative example in 1M KOH; (c) CV curves (d) C dl (e) Nyqusit plot; (f) Stability test plot.

[0026] Figure 3 The images show TEM and SEM images of the MoP@C electrocatalyst prepared in Example 3 of this invention.

[0027] Figure 4 N2 adsorption diagram of the MoP@C electrocatalyst prepared in Example 3 of this invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

[0029] Example

[0030] A method for preparing a MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework includes the following steps: S1. Synthesis of the organic ligand BTPE Under an inert gas atmosphere, 1,2,4-triazole was pre-reacted with a strong base in DMSO solvent at 70°C for 30 minutes to generate 1,2,4-triazole salt. Subsequently, a DMSO solution of 1,5-dibromopentane was slowly added dropwise to the above reaction system, and the reaction was continuously stirred at 75°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, and deionized water was added to precipitate the product. The product was then purified by multiple extractions with an organic solvent. The organic phases were combined, and the solvent was removed by rotary evaporation to obtain a pale yellow viscous liquid product, btpe ligand.

[0031] S2. Synthesis of polymolybdate-based metal-organic framework CUST-698 crystals Sodium molybdate (Na₂MoO₄·2H₂O), cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O), and the btpe ligand prepared in step S1 were accurately weighed and dissolved in a mixed solution of deionized water and concentrated nitric acid. The amount of concentrated nitric acid added was to adjust the pH of the reaction system to 3.0 to form stable polymolybdate anion clusters. The mixed solution was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and crystallized at 130°C for 72 hours using a hydrothermal method. After the reaction, the mixture was cooled to room temperature, and the resulting pink blocky crystals were collected by centrifugation or filtration. The crystals were washed repeatedly with deionized water and ethanol, and then vacuum dried at 60°C to obtain high-purity CUST-698 crystal particles with the molecular formula C. 23 H 30 CoMo5N 16 O 17 .

[0032] In-situ synthesis of S3.MoP@C electrocatalyst a. Preparation of the precursor solution: The CUST-698 crystal particles obtained in step S2 were ground into powder and then dispersed together with phytic acid (PA) in deionized water at a mass ratio of 1:10. The mixture was stirred vigorously at room temperature for 30 minutes. During this process, the phosphate groups in the phytic acid molecules interact strongly with the metal sites in the CUST-698 crystal framework to form a uniform orange-red pre-assembled complex.

[0033] b. Introduction of carbon source: Polyvinylpyrrolidone (PVP) is dissolved in deionized water and added dropwise to the suspension prepared in step a above. Stirring is continued for 6 hours to ensure that PVP molecules are fully coated on the surface of the pre-assembled composite. The mass ratio of PVP to CUST-698 crystal powder in step S3a above is 0.8:1.

[0034] c. Drying and Pyrolysis: The mixture obtained in step b is transferred to a crucible, where most of the moisture is evaporated at 80°C, and then thoroughly dried in a vacuum drying oven at 60°C to obtain a fluffy solid precursor. This solid precursor is placed in a tube furnace and, under an inert protective atmosphere, heated to the target temperature (800°C) at a programmed heating rate of 2°C / min, and held at this temperature for 1 hour for phosphating / carburizing. After the reaction is complete, it is naturally cooled to room temperature to obtain the black final product—the MoP@C electrocatalyst.

[0035] The MoP@C electrocatalyst is used in the electrocatalytic hydrogen evolution electrode.

[0036] Example

[0037] A method for preparing a MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework includes the following steps: S1. Synthesis of the organic ligand BTPE Under an inert gas atmosphere, 1,2,4-triazole was pre-reacted with a strong base in DMSO solvent at 90°C for 60 minutes to generate 1,2,4-triazole salt. Subsequently, a DMSO solution of 1,5-dibromopentane was slowly added dropwise to the above reaction system, and the reaction was continuously stirred at 85°C for 12 hours. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to precipitate the product, and the product was purified by multiple extractions with an organic solvent. The organic phases were combined, and the solvent was removed by rotary evaporation to obtain a pale yellow viscous liquid product, btpe.

[0038] S2. Synthesis of polymolybdate-based metal-organic framework CUST-698 crystals Sodium molybdate (Na₂MoO₄·2H₂O), cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O), and the btpe ligand prepared in step S1 were accurately weighed and dissolved in a mixed solution of deionized water and concentrated nitric acid. The amount of concentrated nitric acid added was to adjust the pH of the reaction system to 4.5. The mixed solution was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and crystallized at 150°C for 72 hours using a hydrothermal method. After the reaction, the mixture was cooled to room temperature, and the resulting pink blocky crystals were collected by centrifugation or filtration. The crystals were washed repeatedly with deionized water and ethanol, and then vacuum dried at 80°C to obtain high-purity CUST-698 crystal particles with the molecular formula C. 23 H 30 CoMo5N 16 O 17 .

[0039] In-situ synthesis of S3.MoP@C electrocatalyst a. Preparation of the precursor solution: The CUST-698 crystal particles obtained in step S2 were ground into powder and then dispersed together with phytic acid (PA) in deionized water at a mass ratio of 1:14. The mixture was stirred vigorously at room temperature for 60 minutes. During this process, the phosphate groups in the phytic acid molecules interact strongly with the metal sites in the CUST-698 crystal framework to form a uniform orange-red pre-assembled complex.

[0040] b. Introduction of carbon source: Polyvinylpyrrolidone (PVP) is dissolved in deionized water and added dropwise to the suspension prepared in step a above. Stirring is continued for 10 hours to ensure that PVP molecules are fully coated on the surface of the pre-assembled composite. The mass ratio of PVP to CUST-698 crystal powder in step S3a above is 1.2:1.

[0041] c. Drying and Pyrolysis: The mixture obtained in step b is transferred to a crucible, where most of the moisture is evaporated at 100°C, followed by thorough drying in a vacuum drying oven at 80°C to obtain a fluffy solid precursor. This solid precursor is placed in a tube furnace and, under an inert protective atmosphere, heated to the target temperature (950°C) at a programmed heating rate of 10°C / min, and held at this temperature for 3 hours for phosphating / carburizing. After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain the black final product—the MoP@C electrocatalyst.

[0042] The MoP@C electrocatalyst or the electrocatalytic hydrogen evolution electrode using the MoP@C electrocatalyst is used in the hydrogen evolution reaction (HER) in an acidic electrolyte.

[0043] Example

[0044] A method for preparing a MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework includes the following steps: S1. Synthesis of the organic ligand BTPE Under an inert gas atmosphere, 1,2,4-triazole was pre-reacted with a strong base in DMSO solvent at 90°C for 60 minutes to generate 1,2,4-triazole salt. Subsequently, a DMSO solution of 1,5-dibromopentane was slowly added dropwise to the above reaction system, and the reaction was continuously stirred at 85°C for 12 hours. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to precipitate the product, and the product was purified by multiple extractions with an organic solvent. The organic phases were combined, and the solvent was removed by rotary evaporation to obtain a pale yellow viscous liquid product, btpe ligand.

[0045] S2. Synthesis of polymolybdate-based metal-organic framework CUST-698 crystals Sodium molybdate (Na₂MoO₄·2H₂O), cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O), and the btpe ligand prepared in step S1 were accurately weighed and dissolved in a mixed solution of deionized water and concentrated nitric acid. The amount of concentrated nitric acid added was to adjust the pH of the reaction system to 4.5 to form stable polymolybdate anion clusters. The mixed solution was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and crystallized at 150°C for 72 hours using a hydrothermal method. After the reaction, the mixture was cooled to room temperature, and the resulting pink blocky crystals were collected by centrifugation or filtration. The crystals were washed repeatedly with deionized water and ethanol, and then vacuum dried at 80°C to obtain high-purity CUST-698 crystal particles with the molecular formula C. 23 H 30 CoMo5N 16 O 17 .

[0046] In-situ synthesis of S3.MoP@C electrocatalyst a. Preparation of the precursor solution: The CUST-698 crystal particles obtained in step S2 were ground into powder and then dispersed together with phytic acid (PA) in deionized water at a mass ratio of 1:12. The mixture was stirred vigorously at room temperature for 60 minutes. During this process, the phosphate groups in the phytic acid molecules interact strongly with the metal sites in the CUST-698 crystal framework to form a uniform orange-red pre-assembled complex.

[0047] b. Introduction of carbon source: Polyvinylpyrrolidone (PVP) is dissolved in deionized water and added dropwise to the suspension prepared in step a above. Stirring is continued for 10 hours to ensure that PVP molecules are fully coated on the surface of the pre-assembled composite. The mass ratio of PVP to CUST-698 crystal powder in step S3a above is 1:1.

[0048] c. Drying and Pyrolysis: The mixture obtained in step b is transferred to a crucible, where most of the moisture is evaporated at 100°C, followed by thorough drying in a vacuum drying oven at 80°C to obtain a fluffy solid precursor. This solid precursor is placed in a tube furnace and, under an inert protective atmosphere, heated to the target temperature (900°C) at a programmed heating rate of 10°C / min, and held at this temperature for 3 hours for phosphating / carburizing. After the reaction is complete, it is naturally cooled to room temperature to obtain the black final product—the MoP@C electrocatalyst.

[0049] The MoP@C electrocatalyst or the electrocatalytic hydrogen evolution electrode using the MoP@C electrocatalyst is used in the hydrogen evolution reaction (HER) in an alkaline electrolyte.

[0050] Comparative Example 1 Comparative Example 1 is a MoP@C-2 electrocatalyst synthesized by adding CUST-698 crystals and phytic acid to existing technologies and sintering at 900℃.

[0051] Comparative Example 2 Comparative Example 2 is a CoMoO4@C electrocatalyst synthesized by adding CUST-698 crystals and PVP at a sintering temperature of 900℃ in the prior art.

[0052] Comparative Example 3 Comparative Example 3 is a CoMoO4 electrocatalyst synthesized using only CUST-698 crystals at a sintering temperature of 900℃ in the prior art.

[0053] Comparative Example 4 Comparative Example 4 is an existing Pt / C electrocatalyst.

[0054] The polarization curves of the MoP@C electrocatalyst and the electrocatalyst in the comparative example in 0.5 M H2SO4 solution are shown below. Figure 1As shown in Figure a, it can be seen that the Pt / C electrocatalyst still exhibits the best hydrogen evolution performance when the current density reaches 1 mA / cm². -2 At that time, the overpotential of the MoP@C electrocatalyst was 190 mV, which was higher than that of the MoP@C-2 electrocatalyst (280 mV) and the CoMoO4@C electrocatalyst (297 mV). The performance of the CoMoO4 electrocatalyst was extremely poor, with a current density that did not reach 1 mA / cm². -2 . Figure 1 b is the relevant Tafel slope plot; the Tafel slope of the Pt / C electrocatalyst is only 17 mVdec in acidic medium. -1 This conforms to the Volmer-Tafel reaction mechanism, and the Tafel slope of the MoP@C electrocatalyst is 75 mVdec. -1 The reaction follows the Volmer-Heyrovsky mechanism, with the Volmer step as the rate-determining step. The Tafel slopes of the MoP@C-2 and CoMoO4@C electrocatalysts are greater than those of the MoP@C electrocatalyst. In contrast, the MoP@C electrocatalyst exhibits superior hydrogen evolution performance, indicating that the phase composition of the MoP@C electrocatalyst and the protective effect of graphite carbon on the nanoparticles are beneficial to improving the catalyst's hydrogen evolution performance. To obtain the electrochemically active specific surface area (ECSA), in 0.5 M H2SO4, by utilizing different scan rates (5 mV / s)... -1 ~250mVs -1 The electrochemical double-layer capacitance was tested using cyclic voltammetry. C dl ), Figure 1 c represents the MoP@C electrocatalyst at 5mVs. -1 ~250mVs -1 CV curves within the range Figure 1 d represents the MoP@C electrocatalyst and the comparative electrocatalyst at 5 mV / s. -1 ~250mVs -1 Within range C dl Value graph, by Figure 1 As can be seen from d, the MoP@C electrocatalyst... C dl The value is 14.63 mFcm -2 It is far greater than that of the MoP@C-2 electrocatalyst (3.22 mFcm). -2 ) and CoMoO4@C electrocatalyst (6.34 mFcm) -2 )of. Figure 1 c and Figure 1 The results show that the MoP@C electrocatalyst has a high electrochemically active specific surface area and can provide more catalytic active sites in the electrocatalytic hydrogen evolution process, thereby promoting the HER performance of the catalyst.

[0055] Electrochemical impedance spectroscopy (EIS) can observe charge transfer on the surface of electrocatalysts, thus measuring their performance. Figure 1 It can be known that the current density is 1 mA / cm². -2 The Nyquist plots of MoP@C electrocatalyst, MoP@C-2 electrocatalyst, and CoMoO4@C electrocatalyst are shown below. Figure 1 As shown in e, the charge transfer impedance of the MoP@C electrocatalyst can be clearly seen. R ct The charge transfer rate of the MoP@C electrocatalyst is significantly lower than that of the comparative electrocatalyst, indicating that the MoP@C electrocatalyst has a higher charge transfer rate. Furthermore, the stability of the MoP@C electrocatalyst was tested in 0.5 M H₂SO₄ using a chronoamperometry method. Figure 1 As shown in f, the current-time (it) curve remained almost unchanged over 24 hours, indicating that the MoP@C electrocatalyst exhibits excellent stability for up to 24 hours.

[0056] Depend on Figure 2 It can be seen that in alkaline media, the MoP@C electrocatalyst at 1 mA cm⁻¹ -2 The overpotential is 208 mV, and the Tafel slope is 96 mVdec. -1 The catalytic activity of MoP@C electrocatalyst in alkaline media is far lower than that of the comparative electrocatalyst. Although the catalytic activity of MoP@C electrocatalyst in alkaline media is not as good as that of Pt / C electrocatalyst, it is highly competitive with other synthetic metal carbides due to its inherent advantages. Meanwhile, the Tafel slope and double-layer capacitance (20.59 mF / cm²) of MoP@C electrocatalyst in alkaline electrolyte solution are significantly lower. -2 The impedance and stability also show similar trends. The MoP@C electrocatalyst exhibits better hydrogen evolution reaction activity in alkaline media than the comparative electrocatalyst.

[0057] Figure 3 TEM images show that the MoP@C electrocatalyst exhibits a cross-linked plate-like structure, forming abundant macropores and mesopores. Figure 3 TEM images of a further confirm that ultrafine nanoparticles (mainly 40 nm to 120 nm in size) are uniformly encapsulated in a transparent carbon layer. Figure 3 Clear lattice fringes can be observed in the HRTEM image of b, with a crystal plane spacing of 0.114 nm, corresponding to the (112) crystal plane of MoP. Figure 3 The elemental mapping diagrams of c, d, e, f, g, and h show that the five elements C, N, P, Mo, and Co are highly uniformly co-distributed in the material, demonstrating the advantages of molecular-level mixing in precursor MOFs.

[0058] Figure 4The N2 adsorption-desorption isotherm of the MoP@C electrocatalyst is type IV, accompanied by an H3-type hysteresis loop, indicating the presence of numerous mesopores in the material. Its BET specific surface area is 277 m² / g. The pore size distribution diagram shown in the figure confirms the simultaneous presence of mesopores ranging from 2 nm to 5 nm and a small number of micropores smaller than 2 nm. This hierarchical pore structure greatly facilitates the mass transfer process.

[0059] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0060] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework, characterized in that: Includes the following steps: S1. Synthesis of the organic ligand BTPE Under inert gas protection, 1,2,4-triazole was pre-reacted with a strong base in a polar aprotic solvent at 70°C–90°C for 30–60 minutes to generate 1,2,4-triazole salt. Subsequently, a solution of 1,5-dibromopentane was slowly added dropwise to the above reaction system, and the reaction was continuously stirred at 75°C–85°C for 8–12 hours. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to precipitate the product, and the product was extracted multiple times with an organic solvent. The organic phases were combined, and the solvent was removed by rotary evaporation to obtain a pale yellow viscous liquid product, btpe ligand. S2. Synthesis of polymolybdate-based metal-organic framework CUST-698 crystals Sodium molybdate, cobalt nitrate hexahydrate, and the btpe ligand prepared in step S1 were accurately weighed and dissolved in a mixed solution of deionized water and concentrated nitric acid. The amount of concentrated nitric acid added was to adjust the pH of the reaction system to 3.0-4.

5. The mixed solution was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and crystallized at 130-150°C for 72 hours by hydrothermal method. After the reaction was completed, the temperature was cooled to room temperature by program. The resulting pink blocky crystals were collected by centrifugation or filtration and washed repeatedly with deionized water and ethanol. The crystals were then dried under vacuum at 60-80°C to obtain high-purity CUST-698 crystal particles. In-situ synthesis of S3.MoP@C electrocatalyst a. Preparation of precursor solution: The CUST-698 crystal particles obtained in step S2 were ground into powder and then dispersed together with phytic acid in deionized water. The mixture was stirred vigorously at room temperature for 30 to 60 minutes. b. Introduction of carbon source: Dissolve polyvinylpyrrolidone in deionized water and add it dropwise to the suspension prepared in step a above, and continue stirring for 6 to 10 hours; c. Drying and pyrolysis: The mixture obtained in step b is transferred to a crucible and evaporated at 80℃~100℃ to remove most of the moisture. Then, it is thoroughly dried in a vacuum drying oven at 60℃~80℃ to obtain a fluffy solid precursor. The solid precursor is placed in a tube furnace and heated to the target temperature of 800℃~950℃ (the sintering temperature) at a heating rate of 2℃ / min~10℃ / min under an inert protective atmosphere. The temperature is then maintained at this rate for 1 hour~3 hours for phosphating / carbonization reaction. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the black final product, MoP@C electrocatalyst.

2. The method for preparing the MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework according to claim 1, characterized in that: The mass ratio of CUST-698 crystal powder to phytic acid is 1:10 to 1:

14.

3. The method for preparing the MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework according to claim 2, characterized in that: The mass ratio of CUST-698 crystal powder to phytic acid is 1:

12.

4. The method for preparing the MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework according to claim 1, characterized in that: The mass ratio of polyvinylpyrrolidone to CUST-698 crystal powder is 0.8:1 to 1.2:

1.

5. The method for preparing the MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework according to claim 4, characterized in that: The mass ratio of polyvinylpyrrolidone to CUST-698 crystal powder is 1:

1.

6. The method for preparing the MoP@C electrocatalyst based on a polymolybdate-based metal-organic framework according to claim 1, characterized in that: The target temperature is 900℃.

7. A MoP@C electrocatalyst, characterized in that: The MoP@C electrocatalyst is prepared by the method described in any one of claims 1 to 6.

8. An application of a MoP@C electrocatalyst, characterized in that: The MoP@C electrocatalyst described in claim 7 is applied to the electrocatalytic hydrogen evolution electrode.

9. The application of the MoP@C electrocatalyst according to claim 8, characterized in that: The MoP@C electrocatalyst or electrocatalytic hydrogen evolution electrode described in claim 8 is used in hydrogen evolution reactions in acidic or alkaline electrolytes.

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