An electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, its preparation method and application

Abstract

This invention discloses an electrocatalytic composite material based on cobalt single-atom-controlled molybdenum carbide phase transition, its preparation method, and its application, relating to the field of electrocatalytic hydrogen production technology. The preparation method includes: dispersing a cobalt source, a molybdenum source, and a surfactant in water, adjusting the solution to acidity to obtain a reaction solution; placing a substrate in the reaction solution and reacting at 150-250℃ for 4-8 hours to obtain a precursor; placing the precursor and a carbon source under an inert atmosphere, heating at 3-7℃ / min to 800-1000℃ and holding for 1-3 hours to obtain the electrocatalytic composite material; in the reaction solution, the molar ratio of molybdenum to cobalt is 1:(0.01-0.33); the molar ratio of molybdenum to carbon source is 1:(0.01-0.03). This invention employs hydrothermal synthesis and high-temperature carbonization, precisely controlling the phase structure of the carbide through cobalt single atoms to optimize electronic structure and catalytic performance, thereby enabling water electrolysis applications across the entire pH range.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic hydrogen production technology, and in particular to an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, its preparation method, and its application. Background Technology

[0002] Electrolysis of water to produce hydrogen is the core technology for the preparation of "green hydrogen," but its large-scale application is limited by the development of efficient, stable, inexpensive, and universally applicable electrocatalytic materials.

[0003] Currently, while platinum-based catalytic materials exhibit excellent performance, their scarcity and high cost constitute major bottlenecks. In contrast, transition metal carbides, especially molybdenum-based carbides (such as molybdenum carbide (MoC) and molybdenum dicarbide (Mo2C)), are considered highly promising alternative materials due to their unique d-electron structure, platinum-like hydrogen adsorption properties, and good electrical conductivity.

[0004] However, single molybdenum-based carbide phases suffer from insufficient intrinsic activity, limited active sites, and poor stability under harsh electrolytic conditions (especially acidic conditions). Although MoC / Mo2C composites can optimize electronic structure, enhance charge transfer, and stabilize active interfaces by constructing two-phase heterostructures, existing preparation methods (such as temperature-programmed carbonization) do not provide precise control over the ratio of the two phases, grain boundaries, and interfacial coupling, resulting in limited built-in electric fields and synergistic effects, thus hindering performance improvement.

[0005] Therefore, existing technologies still need improvement and development. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide an electrocatalytic composite material based on cobalt single-atom-regulated molybdenum carbide phase transition, its preparation method and application, aiming to solve the problems of excessive hydrogen adsorption, low active site density and unstable phase structure of existing molybdenum carbide-based electrocatalytic materials.

[0007] The technical solution of the present invention is as follows: In a first aspect, a method for preparing an electrocatalytic composite material based on cobalt single-atom-regulated molybdenum carbide phase transition is provided, comprising the following steps: A cobalt source, a molybdenum source, and a surfactant are dispersed in water, and the pH is adjusted to acidity to obtain a reaction solution. The substrate was placed in the reaction solution and reacted at 150-250°C for 4-8 hours to obtain the precursor. The precursor and carbon source were placed in an inert atmosphere and heated to 800-1000℃ at a heating rate of 3-7℃ / min and held for 1-3 hours to obtain an electrocatalytic composite material. In the reaction solution, the molar ratio of molybdenum to cobalt is 1:(0.01~0.33). The amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.01~0.03).

[0008] In a preferred embodiment, the molar ratio of molybdenum to cobalt in the reaction solution is 1:(0.05~0.12).

[0009] In a preferred embodiment, the cobalt source is selected from one or more of cobalt chloride, cobalt nitrate, cobalt acetate, cobalt sulfate, and cobalt oxalate.

[0010] In a preferred embodiment, the molybdenum source is selected from one or more of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and ammonium phosphomolybdate.

[0011] In a preferred embodiment, the molar ratio of molybdenum to surfactant in the reaction solution is 1:(0.01~1).

[0012] In a preferred embodiment, the surfactant is selected from one or more of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfate.

[0013] In a preferred embodiment, the amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.015~0.02).

[0014] In a preferred embodiment, the carbon source is selected from one or more of dicyandiamide, melamine, and cyanamide.

[0015] In a preferred embodiment, the acidity refers to a pH of 1 to 2.

[0016] In a preferred embodiment, the substrate is carbon cloth.

[0017] In a further preferred embodiment, the carbon cloth undergoes pretreatment; The preprocessing includes the following steps: The carbon was placed in nitric acid and reacted at 130-150°C for 8-12 hours. After removal, it was washed.

[0018] In a preferred embodiment, the inert atmosphere is nitrogen.

[0019] In a second aspect, an electrocatalytic composite material based on cobalt single-atom-regulated molybdenum carbide phase transition is provided, which is prepared using the preparation method described in the first aspect.

[0020] Thirdly, the application of the electrocatalytic composite material described in the second aspect in the hydrogen evolution reaction is provided.

[0021] Beneficial effects: This invention provides a method for preparing electrocatalytic composite materials based on cobalt single-atom-controlled molybdenum carbide phase transition. Compared with existing technologies, its advantages are as follows: (1) Precise “phase-atom” synergistic control: This invention utilizes cobalt single atoms to achieve precise construction of MoC / Mo2C heterojunction.

[0022] (2) Excellent performance across all pH levels: The electrocatalytic composite material prepared by this invention has a unique structure and can maintain top hydrogen evolution reaction activity and stability in acidic, neutral and alkaline environments. It is a "general-purpose" catalytic material that is suitable for a variety of electrolysis technology routes.

[0023] (3) High stability: The electrocatalytic composite material prepared by the present invention effectively inhibits the aggregation, dissolution and phase separation of the active components through cobalt single-atom anchoring, ensuring the reliability of long-term operation.

[0024] (4) Method scalability: The preparation process of the present invention is relatively simple, the parameters are controllable, and it has the potential for large-scale production. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the technical principle of the present invention.

[0026] Figure 2 The images show the XRD patterns of the electrocatalytic composite materials prepared in Examples 1-5 and Comparative Example 1.

[0027] Figure 3 These are morphological and structural analysis diagrams of the electrocatalytic composite material (Co-MoC / Mo2C) prepared in Example 1.

[0028] Figure 4 The figures show the XPS spectra and calculated ratios of the two phases MoC and Mo2C for the electrocatalytic composite material prepared in Example 1 (Mo:Co=1:0.1), the electrocatalytic composite material prepared in Example 4 (Mo:Co=1:0.2), and the electrocatalytic composite material prepared in Comparative Example 1 (Mo:Co=1:0).

[0029] Figure 5 The graph shows the electrochemical test results of the electrocatalytic composite material (Co-MoC / Mo2C) prepared in Example 1, the electrocatalytic composite material (Co-Mo2C) prepared in Example 4, and the precursor (Co-MoO3) prepared in Example 1 under alkaline conditions.

[0030] Figure 6The graph shows the electrochemical test results of the electrocatalytic composite material (Co-MoC / Mo2C) prepared in Example 1, the electrocatalytic composite material (Co-Mo2C) prepared in Example 4, and the precursor (Co-MoO3) prepared in Example 1 under acidic conditions.

[0031] Figure 7 The graph shows the electrochemical test results of the electrocatalytic composite material (Co-MoC / Mo2C) prepared in Example 1, the electrocatalytic composite material (Co-Mo2C) prepared in Example 4, and the precursor (Co-MoO3) prepared in Example 1 under neutral conditions. Detailed Implementation

[0032] This invention provides an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below.

[0033] Electrocatalytic materials are crucial for hydrogen production through water electrolysis, but existing electrocatalytic materials suffer from the following drawbacks: (1) Activity, stability and cost are difficult to balance: precious metal catalytic materials are limited by cost and stability; non-precious metal catalytic materials cannot match precious metals in both activity and overall pH stability.

[0034] (2) The phase structure regulation is rough and the interface effect is not maximized: The existing methods for preparing MoC / Mo2C composite materials (such as temperature-programmed carbonization) do not have precise control over the ratio of the two phases, grain boundaries and interface coupling, resulting in limited built-in electric field and synergistic effect, and performance improvement encounters a bottleneck.

[0035] (3) The contradiction between the density of active sites and intrinsic activity: increasing the loading often leads to the atom agglomeration to form nanoparticles, reducing the atom utilization rate; while maintaining the single-atom morphology often faces the problems of low loading and insufficient total number of active sites.

[0036] (4) Insufficient adaptability across pH range: Most high-performance catalytic materials only perform well within a specific pH range. For example, many carbides are relatively active in alkaline conditions but unstable in acidic conditions; while some acid-stable catalytic materials experience a sharp drop in activity in neutral / alkaline conditions. There is a lack of "universal" catalytic materials that can maintain high activity and high stability in all pH media.

[0037] (5) The preparation process is complex and difficult to scale up: Many synthesis methods involving fine nanostructures or single-atom anchoring are complicated, have harsh conditions (such as the use of strong etchants and multi-step high-temperature treatment), and have poor reproducibility, which hinders their industrial application.

[0038] To systematically address the aforementioned shortcomings, this invention employs a strategy combining precise "phase engineering" and "single-atom engineering" to dually optimize the structure and electronic properties of electrocatalytic materials at both the atomic and nanoscale levels. This results in the preparation of a novel non-precious metal electrolytic water electrolysis hydrogen production catalytic material that possesses high intrinsic activity, high-density active sites, excellent charge transport capability, and outstanding stability across all pH levels.

[0039] Phase engineering—specifically, the precise control of the ratio, distribution, and interfacial coupling of the MoC and Mo2C phases—is a key strategy for breaking through the performance limits of electrocatalytic materials. By constructing a two-phase heterostructure (heterojunction), the electronic structure is optimized, charge transfer is enhanced, and the active interface is stabilized. Building upon this, cobalt single atoms are introduced for further "control," utilizing the strong electronic interactions between atomically dispersed cobalt species and the molybdenum carbide support to achieve deeper electronic state modification of the phase structure and create active sites. This "single-atom-controlled phase structure" strategy synergistically addresses multiple challenges related to intrinsic activity, site density, and structural stability, providing a novel material design approach for developing next-generation universally applicable hydrogen production catalysts across all pH levels.

[0040] Specifically, embodiments of the present invention provide a method for preparing an electrocatalytic composite material based on cobalt single-atom-regulated molybdenum carbide phase transition, comprising the following steps: (1) Disperse the cobalt source, molybdenum source and surfactant in water, adjust the pH to acidic, and obtain a reaction solution; (2) Place the substrate in the reaction solution and react at 150~250℃ for 4~8h to obtain the precursor; (3) The precursor and carbon source are placed in an inert atmosphere and heated to 800-1000℃ at a heating rate of 3-7℃ / min and kept at that temperature for 1-3h to obtain an electrocatalytic composite material. In the reaction solution, the molar ratio of molybdenum to cobalt is 1:(0.01~0.33). The amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.01~0.03).

[0041] In this embodiment, a hydrothermal synthesis and high-temperature carbonization process is employed to introduce isolated cobalt single atoms into the molybdenum carbide (MoC) and molybdenum dicarbide (Mo2C) lattices. The strong electron interaction between Co and Mo is used to induce a directional phase transition in molybdenum carbide, constructing a cobalt single-atom-molybdenum carbide heterogeneous catalytic material. This material can optimize the H* adsorption-desorption energy barrier and expose high-density active sites, achieving breakthroughs in high activity, high stability, and low cost, providing key material support for energy conversion technologies.

[0042] The core innovation of this embodiment lies in overcoming the technical bottlenecks of existing molybdenum carbide-based hydrogen evolution reaction (HER) catalytic materials, such as the difficulty in precisely controlling the phase composition and insufficient catalytic activity and stability. Figure 1 As shown, by using cobalt single atoms as precise control units, a reversible and controllable phase transition between MoC and Mo2C is achieved. Through the directional control of the phase structure, the electronic structure, the number of exposed active sites, and the interfacial interaction of the catalytic material are optimized, ultimately significantly improving its catalytic activity, stability, and durability in HER.

[0043] Compared to existing technologies, this embodiment does not require complex control equipment. By doping / loading cobalt single atoms, the precise switching between MoC and Mo2C phases can be achieved. Moreover, the control process is mild and controllable. At the same time, cobalt single atoms and MoC / Mo2C form a synergistic effect, further enhancing the HER catalytic kinetics and breaking through the performance limitations of single-phase catalytic materials.

[0044] In some embodiments, step (2) is preferably: placing the substrate in the reaction solution and reacting at 180~220°C for 5~7 hours to obtain the precursor.

[0045] In some embodiments, step (3) is preferably: placing the precursor and carbon source in an inert atmosphere, heating to 850-950°C at a heating rate of 4-6°C / min and holding at that temperature for 1.5-2.5h to obtain an electrocatalytic composite material.

[0046] In some embodiments, the molar ratio of molybdenum to cobalt in the reaction solution is 1:(0.05~0.12), preferably 1:(0.067~0.1), more preferably 1:0.1, but not limited thereto. Specifically, in the embodiments of the present invention, the range of molar ratio of molybdenum to cobalt of 1:(0~0.33) was explored, and it was found that the molar ratio of 1:0.1 yielded the best results.

[0047] In some embodiments, the cobalt source is selected from one or more of cobalt chloride (CoCl2), cobalt nitrate (Co(NO3)2), cobalt acetate (Co(CH3COO)2), cobalt sulfate (CoSO4), and cobalt oxalate (CoC2O4), or their crystalline hydrates, but is not limited thereto.

[0048] In some embodiments, the molybdenum source is selected from ammonium molybdate ((NH4)6Mo7O). 24 Sodium molybdate (Na2MoO4), phosphomolybdic acid (H3PMo) 12 O 40 ) and ammonium phosphomolybdate ((NH4)3PMo 12 O 40 One or more of the following, or their crystalline hydrates, but not limited thereto.

[0049] In some embodiments, the molar ratio of molybdenum to the surfactant in the reaction solution is 1:(0.01~1), preferably 1:(0.5~1), more preferably 1:(0.7~0.8), but is not limited thereto.

[0050] In some embodiments, the surfactant is selected from one or more of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfate, but is not limited thereto.

[0051] In some embodiments, the amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.015~0.02), more preferably 1:0.017, but not limited thereto. Specifically, in preliminary experiments without the introduction of cobalt, the present invention explored the range of molar ratio of molybdenum to carbon source being 1:(0.017~0.085), and found that a molar ratio of 1:0.017, for example using 10 mmol ammonium molybdate (70 mmol molybdenum) and 0.1 g (1.19 mmol) dicyandiamide, can generate MoC / Mo2C with optimal performance.

[0052] In some embodiments, the carbon source is selected from one or more of dicyandiamide, melamine, and cyanamide, but is not limited thereto.

[0053] In some embodiments, the acidity refers to a pH of 1 to 2, but is not limited thereto. Specifically, in preliminary experiments, the present invention explored a pH range of 1 to 7 and found that the effect was best at a pH of 1 to 2.

[0054] In some embodiments, the substrate is carbon cloth. Specifically, carbon cloth, i.e., carbon fiber cloth, provides support in this embodiment and is a conventional commercially available product.

[0055] In some more specific embodiments, the carbon cloth undergoes pretreatment; the pretreatment includes the steps of: placing the carbon cloth in nitric acid, reacting at 130-150°C for 8-12 hours, and then removing and washing it. Specifically, the nitric acid (HNO3), as a strong oxidizing agent, can oxidize the surface of the carbon cloth under hydrothermal conditions at 130-150°C, and the oxygen-containing groups are polar, which can improve hydrophilicity.

[0056] In some embodiments, the inert atmosphere is nitrogen, but it is not limited to this.

[0057] In some specific embodiments, a method for preparing an electrocatalytic composite material based on cobalt single-atom-controlled molybdenum carbide phase transition includes the following steps: Cobalt source, molybdenum source and surfactant are dispersed in water, and the pH is adjusted to 1-2 to obtain a reaction solution; The substrate was placed in the reaction solution and reacted at 180-220°C for 5-7 hours to obtain the precursor. The precursor and carbon source were placed in an inert atmosphere and heated to 850-950°C at a heating rate of 4-6°C / min and held at that temperature for 1.5-2.5 h to obtain the electrocatalytic composite material. In the reaction solution, the molar ratio of molybdenum to cobalt is 1:(0.067~0.1). The amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.015~0.02).

[0058] This invention also provides an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, which is prepared using the preparation method described above.

[0059] Specifically, the above preparation method uses a hydrothermal synthesis method (reaction at 150~250℃ for 4~8 hours) and a high-temperature carbonization method (holding at 800~1000℃ for 1~3 hours) to anchor cobalt single atoms onto the carbides. Through the cobalt single atom anchoring strategy, the phase structure of the transition metal carbides (MoC / Mo2C) is precisely controlled to optimize their electronic structure and catalytic performance, enabling the application of water electrolysis at all pH levels under high service current conditions.

[0060] The electrocatalytic composite material prepared by the method specifically includes: (1) a support: the support is a MoC / Mo2C heterojunction; the MoC and Mo2C phases are not simply physically mixed, but are connected through a coherent or semi-coherent interface to form a rich phase interface. The Mo2C phase tends to provide strong hydrogen adsorption sites, while the MoC phase has better conductivity and structural stability. The two work together to form a built-in electric field at the interface, driving the charge to transfer rapidly from the MoC to the Mo2C side. (2) an active center: cobalt exists in the form of single atoms, and these cobalt single atoms preferentially anchor to the interface defects and lattice edges of the MoC / Mo2C heterojunction. There is a strong d-electron orbital interaction between the cobalt single atoms and the support, thereby regulating the local electron density of the MoC / Mo2C heterojunction interface and optimizing the hydrogen adsorption free energy.

[0061] This invention also provides an application of the electrocatalytic composite material described above in the hydrogen evolution reaction.

[0062] In some embodiments, the hydrogen evolution reaction is carried out in an acidic, alkaline, or neutral environment.

[0063] In some embodiments, the electrocatalytic composite material is used as an electrode for the hydrogen evolution reaction, but is not limited thereto.

[0064] In some embodiments, the hydrogen evolution reaction is used in water electrolysis to produce hydrogen or in fuel cells, but is not limited thereto.

[0065] The present invention will be further illustrated below with specific embodiments. Unless otherwise stated, all reagents used in the embodiments are conventional commercially available products.

[0066] Example 1 This embodiment provides an electrocatalytic composite material based on cobalt single-atom-controlled molybdenum carbide phase transition, wherein the molar ratio of Mo to Co is 1:0.1. The specific preparation method is as follows: (1) Substrate pretreatment Cut the carbon cloth into rectangles (2cm × 3cm) and place them in a PTFE-lined high-pressure reactor (100mL volume). Then add 30mL of concentrated nitric acid to completely immerse the carbon cloth in the concentrated nitric acid. Maintain the reactor at 140℃ for 10 hours using hydrothermal heating. After cooling to room temperature, remove the reactor and rinse off any residual nitric acid with water and then with ethanol. Seal the reactor and store it in anhydrous ethanol for later use.

[0067] (2) Synthesis of precursors Weigh out 7 mmol of cobalt chloride hexahydrate (CoCl2) . 6H2O), 10 mmol ammonium molybdate ((NH4)6Mo7O) 24 Disperse the product in 15 mL of deionized water and stir at room temperature for 30 min until completely dissolved. Then add 50 mmol of sodium dodecyl sulfonate to the solution and continue stirring at room temperature for 30 min until dissolved. Adjust the pH to acidic (pH=1~2) with hydrochloric acid. Then quickly transfer the obtained solution to a high-pressure reactor (volume of 20 mL) with a polytetrafluoroethylene liner. Then take the pretreated carbon cloth from step (1) and put it into the high-pressure reactor. After sealing the high-pressure reactor, put it into an oven and perform a hydrothermal reaction at 200℃ for 6 hours. After the reaction is completed, take out the above product, wash it several times with deionized water and ethanol, and dry it in an oven at 60℃ for 12 hours to obtain the precursor.

[0068] (3) Synthesis of electrocatalytic composite materials The precursor prepared in step (2) is placed on one side of a ceramic boat, and 0.1 g (1.19 mmol) of dicyandiamide is placed on the other side of the ceramic boat. Then it is transferred to a tube furnace and heated to 900 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and held for 2 h. After natural cooling, it is taken out to obtain the electrocatalytic composite material.

[0069] Example 2 This embodiment provides an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, wherein the molar ratio of Mo to Co is 1:0.067. The preparation method is the same as in Example 1, except that the molar ratio of Mo to Co is adjusted by changing the amount of cobalt chloride hexahydrate; the amounts of other substances and the preparation steps remain unchanged.

[0070] Example 3 This embodiment provides an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, wherein the molar ratio of Mo to Co is 1:0.125. The preparation method is the same as in Example 1, except that the molar ratio of Mo to Co is adjusted by changing the amount of cobalt chloride hexahydrate; the amounts of other substances and the preparation steps remain unchanged.

[0071] Example 4 This embodiment provides an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, wherein the molar ratio of Mo to Co is 1:0.2. The preparation method is the same as in Example 1, except that the molar ratio of Mo to Co is adjusted by changing the amount of cobalt chloride hexahydrate; the amounts of other substances and the preparation steps remain unchanged.

[0072] Example 5 This embodiment provides an electrocatalytic composite material based on cobalt single-atom regulation of molybdenum carbide phase transition, wherein the molar ratio of Mo to Co is 1:0.33. The preparation method is the same as in Example 1, except that the molar ratio of Mo to Co is adjusted by changing the amount of cobalt chloride hexahydrate; the amounts of other substances and the preparation steps remain unchanged.

[0073] Comparative Example 1 This comparative example provides an electrocatalytic composite material without cobalt doping, i.e., the molar ratio of Mo to Co is 1:0. Its preparation method is the same as in Example 1, except that cobalt chloride hexahydrate is not added; the amounts of other substances and the preparation steps remain unchanged.

[0074] The electrocatalytic composite materials prepared in the above embodiments or comparative examples are tested and analyzed below.

[0075] I. X-ray Diffraction Pattern (XRD) Testing XRD analysis was performed on the electrocatalytic composite materials prepared in Examples 1-5 and Comparative Example 1, as well as the precursor of Example 1. The results are as follows: Figure 2 As shown.

[0076] Figure 2In the diffraction pattern, the diffraction peaks at 34.35°, 37.9°, 39.39°, 52.1°, 61.5°, 69.5°, 74.6°, and 75.5° correspond to the (100), (002), (101), (102), (110), (103), (112), and (201) crystal planes of Mo2C (PDF#35-0787), respectively; the three diffraction peaks at 32.1°, 35.7°, and 48.8° correspond to the (001), (100), and (101) crystal planes of MoC (PDF#45-1015), respectively. Figure 2 It can be seen that the introduction of Co modulates the molybdenum carbide phase transition, which indicates that the cobalt single-atom-doped electrocatalytic composite material loaded on a carbon cloth substrate was successfully synthesized in the examples.

[0077] Based on the XRD test results, the electrocatalytic composite material prepared in Example 1 is designated as Co-MoC / Mo2C, the electrocatalytic composite material prepared in Example 4 is designated as Co-Mo2C, and the precursor prepared in Example 1 is designated as Co-MoO3, and subsequent tests are conducted.

[0078] II. Morphological Test The morphology and structure of the electrocatalytic composite material (Co-MoC / Mo2C) prepared in Example 1 were tested and analyzed. The results are as follows: Figure 3 As shown.

[0079] Figure 3 The relevant results and analysis are as follows: like Figure 3 As shown in Figure a, the scanning electron microscope (SEM) image shows that Co-MoC / Mo2C has a three-dimensional hexagonal prism structure.

[0080] like Figure 3 As shown in Figure b, further analysis of the Co-MoC / Mo2C structure by aberration-corrected transmission electron microscopy (AC-TEM) revealed bright single-atom points dispersed between the MoC and Mo2C phases and at the interface between the two phases. Selecting any few regions and combining them with the elemental contrast difference, it can be clearly identified as Co single atoms, proving that Co is highly dispersed in the composite material in the form of single atoms and has not formed nanoparticle agglomerations.

[0081] like Figure 3 As shown in c, for Figure 3 Atomic arrangement line scan analysis of typical regions of MoC and Mo2C revealed that Mo atoms are arranged in a regular and periodic manner in the lattice, while Co atom signals are embedded in the Mo atom array as isolated peaks and are mainly enriched at the two-phase interface. This further clarifies that Co single atoms are selectively distributed at the phase interface and interphase region of MoC and Mo2C, providing a structural basis for the regulation of interface electronic structure and optimization of active sites.

[0082] like Figure 3 As shown in d, defects at the interface between the two phases were observed by AC-TEM to further determine whether cobalt exists in the form of single atoms and its distribution between the two phases. The results show that Co acts as an inducer in the form of single atoms, regulating the controllable phase transition of molybdenum-based carbides from the α phase to the highly active β phase. Furthermore, the presence of defects at the interface between the two phases can accelerate the active sites between heterostructures, optimize the electronic structure, and promote mass transfer.

[0083] like Figure 3 As shown in Figure f, further analysis of the structure of Co-MoC / Mo2C using high-resolution transmission electron microscopy (HR TEM) clearly reveals the interface between the MoC and Mo2C lattice fringes; the magnified image of the area highlighted in red on the left is shown in Figure f. Figure 3 As shown in Figure e, the (101) crystal plane of Mo2C can be observed, with a lattice fringe spacing of 0.229 nm; the magnified view of the area highlighted in blue on the right is shown below. Figure 3 As shown in Figure g, the (100) crystal plane of MoC can be observed, with a lattice fringe spacing of 0.249 nm; this proves that the electrocatalytic composite material is composed of two phases, Mo2C and MoC.

[0084] like Figure 3 As shown in h and i, the elemental surface scan spectra of Co-MoC / Mo2C show the distribution of Co, Mo, C and N elements, further proving the synthesis of Co-MoC / Mo2C.

[0085] The above test results show that Co-MoC / Mo2C was successfully synthesized in Example 1 of this invention.

[0086] III. X-ray photoelectron spectroscopy (XPS) testing To further investigate the electronic structure of the electrocatalytic composite material (Co-MoC / Mo2C, Mo:Co=1:0.1) prepared in Example 1, the surface elemental composition of Co-MoC / Mo2C was systematically characterized by XPS. The electrocatalytic composite material (Co-Mo2C, Mo:Co=1:0.2) prepared in Example 4 and the electrocatalytic composite material (Mo:Co=1:0) prepared in Comparative Example 1 were used as comparisons to demonstrate that Co regulates the molybdenum carbide phase transition. The results are as follows: Figure 4 As shown.

[0087] Figure 4 The relevant results and analysis are as follows: like Figure 4 As shown in Figure a, in the 3d spectrum of Mo, Mo 2+ and Mo 3+ Derived from Mo2C and MoC respectively, Mo 4+ and Mo 6+The characteristic peaks near 228.3 eV and 231.6 eV, respectively, originate from MoO2 and MoO3, and correspond to Mo. 2+ The peaks near 228.7 eV and 232 eV correspond to Mo 3+ The results showed that as the amount of Co added increased, Mo... 3+ The peak area of ​​(MoC) is decreasing significantly, while Mo 2+ The peak area of ​​(Mo2C) is increasing significantly. This indicates that the introduction of Co leads to the transformation of MoC into the Mo2C phase, and different amounts of Co added will result in different ratios between the two phases.

[0088] like Figure 4 As shown in Figure b, in the N 1s spectrum, the characteristic peaks at binding energies of 394.6 eV, 397.9 eV, and 399.6 eV correspond to Mo 3p, pyridinic N, and pyrrolic N, respectively.

[0089] like Figure 4 As shown in Figure c, in the C 1s spectrum, the characteristic peaks at binding energies of 283.5 eV, 284.6 eV, and 285.5 eV correspond to the Mo-C bond, C-C bond, and CN bond, respectively.

[0090] like Figure 4 As shown in Figure d, the ratio of MoC to Mo2C in electrocatalytic composite materials with different molybdenum-cobalt ratios was calculated using the peak area in XPS and Origin.

[0091] The above results indicate that cobalt single atoms act as an inducer to induce the transformation of MoC to the Mo2C phase, precisely controlling the ratio of the two phases and optimizing the catalytic performance.

[0092] IV. Electrochemical Testing The electrocatalytic composite material (Co-MoC / Mo2C) prepared in Example 1 was used as the working electrode, and its hydrogen evolution reaction (HER) performance was tested at all pH values ​​in a three-electrode system. The electrocatalytic composite material (Co-Mo2C) prepared in Example 4 and the precursor (Co-MoO3) prepared in Example 1 were used as comparisons. Electrochemical tests were performed using a Chenhua CHI760E electrochemical workstation, and the performance results of the electrocatalytic composite material were obtained using a three-electrode system.

[0093] (1) HER alkaline medium performance test The three-electrode system consists of an electrode clip (working electrode), a mercury / mercury oxide electrode (reference electrode), a carbon rod (counter electrode), and an electrolyte. The potential conversion formula between the mercury / mercury oxide electrode and the reversible hydrogen electrode (RHE) is: E RHE =E Hg / HgO +0.059pH+0.098.

[0094] A three-electrode system was installed, using a 1.0M potassium hydroxide (KOH) solution as the electrolyte. Co-MoC / Mo2C, Co-Mo2C, and Co-MoO3 samples were cut into 0.5cm × 1.5cm pieces. The cut samples were fixed with electrode clamps, ensuring that the sample immersion area in the liquid was 0.5cm × 0.5cm. Testing then commenced. Cyclic voltammetry (CV) was used to activate the samples at a scan rate of 100 mV·s. -1 After the curves basically overlap, linear sweep voltammetry (LSV) is started at a rate of 5 mV·s. -1 The LSV curve was obtained by reverse scanning within a potential range of (-0.8) to (-1.5) V. The double-layer capacitance (C...) dl The test was conducted within the non-Radar interval, using different scan rates to obtain CV curves. The scan rate was plotted on the x-axis, and the difference between the median values ​​of the intervals was divided by two to obtain the y-axis. The slope obtained after fitting the curves represents the double-layer capacitance. Sample stability data were obtained by controlling the current density (10 mA cm⁻¹) using the chronoamperometry method. -2 100mA cm -2 500mA cm - ²) The test results are as follows. Figure 5 As shown.

[0095] Figure 5 The relevant results and analysis are as follows: like Figure 5 As shown in Figure a, the LSV curves after iR correction show that Co-MoC / Mo2C exhibits excellent catalytic activity at a current density of 10 mA cm⁻¹. -2 500mA cm -2 and 1000mA cm -2 At these times, the overpotentials (η) were as low as 52 mV, 202 mV, and 251 mV, respectively, much lower than those of Co-Mo2C (η10 = 83 mV, η500 = 314 mV, η1000 = 420 mV) and Co-MoO3 (η10 = 209 mV, η500 = 443 mV, η1000 = 542 mV). This is attributed to the interfacial electric field and the Co single atom jointly promoting the water dissociation step.

[0096] like Figure 5 As shown in Figure b, the Tafel slope of Co-MoC / Mo2C is 66.8 mV dec. -1 It is lower than that of Co-Mo2C (98.2 mV dec). -1 ) and Co-MoO3 (104.5mV dec -1This indicates that Co-MoC / Mo2C exhibits excellent catalytic kinetics.

[0097] like Figure 5 As shown in Figure c, the charge transfer rate (Rct) of the above samples was further studied by electrochemical impedance spectroscopy (EIS). The impedance value is negatively correlated with the electron transfer rate. The larger the impedance value, the slower the electron transfer rate of the sample. The results show that the Rct of Co-MoC / Mo2C is smaller than that of Co-Mo2C and Co-MoO3, indicating that Co-MoC / Mo2C has the fastest electron transport rate in the HER catalysis process.

[0098] like Figure 5 As shown in Figure d, the electrochemical activity of different samples was further explored. The double-layer capacitance of the samples was tested at different scan rates in the non-Radida potential region. Then, the C of the samples was obtained by fitting cyclic voltammetry curves. dl The Ca value was used to evaluate its electrochemically active surface area (ECSA); the results showed that the Ca of Co-MoC / Mo2C was significantly higher than that of Mo2C. dl The value is as high as 73.7 mF cm -2 It is significantly superior to Co-Mo2C (53.4 mF cm⁻¹). -2 ) and Co-MoO3 (22.4mF cm -2 ).

[0099] like Figure 5 As shown in Figure e, the calculated Faraday efficiency of Co-MoC / Mo2C in the HER process is 98.4%.

[0100] like Figure 5 As shown in Figure f, current density diagrams under different overpotentials are plotted based on the LSV curves of Co-MoC / Mo2C, Co-Mo2C, and Co-MoO3. It can be seen that Co-MoC / Mo2C has the lowest overpotential under the same current density.

[0101] like Figure 5 As shown in Figure g, the stability of the sample was tested by measuring the amperometric IT curve. The results show that at 10 mA / cm², the stability of the sample is good. -2 100mAcm -2 and 500mAcm -2 Under constant current density, Co-MoC / Mo2C can remain stable for more than 400 hours, indicating that Co-MoC / Mo2C has good electrochemical stability.

[0102] (2) HER acidic medium performance test The three-electrode system consists of an electrode clip (working electrode), a mercury / mercuric chloride electrode (reference electrode), a carbon rod (counter electrode), and an electrolyte. The potential conversion formula between the mercury / mercuric chloride electrode and the reversible hydrogen electrode (RHE) is: ERHE =E Hg / Hg2Cl2 +0.059pH +0.242.

[0103] A three-electrode system was installed, using a 0.5M sulfuric acid (H₂SO₄) solution as the electrolyte. Co-MoC / Mo₂C, Co-Mo₂C, and Co-MoO₃ samples were cut into 0.5cm × 1.5cm pieces. The cut samples were fixed with electrode clamps, ensuring that the sample immersion area in the liquid was 0.5cm × 0.5cm. Testing then commenced. Cyclic voltammetry (CV) was used to activate the samples at a scan rate of 100 mV·s. -1 After the curves basically overlap, linear sweep voltammetry (LSV) is started at a rate of 5 mV·s. -1 The LSV curve was obtained by reverse scanning within a potential range of (0) to (-0.65) V. The double-layer capacitance (C...) dl The test was conducted within the non-Radar interval, using different scan rates to obtain CV curves. The scan rate was plotted on the x-axis, and the difference between the median values ​​of the intervals was divided by two to obtain the y-axis. The slope obtained after fitting the curves represents the double-layer capacitance. Sample stability data were obtained by controlling the current density (10 mA cm⁻¹) using the chronoamperometry method. -2 100mA cm -2 The test results are as follows. Figure 6 As shown.

[0104] Figure 6 The relevant results and analysis are as follows: like Figure 6 As shown in Figure a, the LSV curves after iR correction show that Co-MoC / Mo2C exhibits excellent catalytic activity at a current density of 10 mA cm⁻¹. -2 and 100mA cm -2 At that time, the overpotentials were as low as 27mV and 58mV, respectively, which were much smaller than the overpotentials of Co-Mo2C (η10=150mV, η100=225mV) and Co-MoO3 (η10=273mV, η100=397mV), indicating that the Co single atom effectively prevented the carbide from oxidative corrosion under acidic conditions.

[0105] like Figure 6 As shown in Figure b, the Tafel slope of Co-MoC / Mo2C is 37.9 mV dec. -1 It is lower than that of Co-Mo2C (72.4 mV dec). -1 ) and Co-MoO3 (163.7mV dec -1 This indicates that Co-MoC / Mo2C exhibits excellent catalytic kinetics.

[0106] like Figure 6 As shown in Figure c, the electrochemical activity of different samples was further explored. The double-layer capacitance of the samples was tested at different scan rates in the non-Radida potential region. Then, the C0 of the samples was obtained by fitting cyclic voltammetry curves. dl The Ca value was used to assess its electrochemically active surface area (ECSA); the results showed that the Ca of Co-MoC / Mo2C was significantly higher than that of Mo2C. dl The value is as high as 51.9mF cm -2 It is significantly superior to Co-Mo2C (40.2 mF cm⁻¹). -2 ) and Co-MoO3 (20.4mF cm -2 ).

[0107] like Figure 6 As shown in Figure d, the charge transfer rate (Rct) of the above samples was further studied by electrochemical impedance spectroscopy (EIS). The impedance value is negatively correlated with the electron transfer rate. The larger the impedance value, the slower the electron transfer rate of the sample. The results show that the Rct of Co-MoC / Mo2C is smaller than that of Co-Mo2C and Co-MoO3, indicating that Co-MoC / Mo2C has the fastest electron transport rate in the HER catalysis process.

[0108] like Figure 6 As shown in e, at 10mA cm -2 Under constant current density, Co-MoC / Mo2C can maintain stability for more than 400 hours.

[0109] like Figure 6 As shown in f, at 100mA cm -2 Under constant current density, Co-MoC / Mo2C can maintain stability for more than 200 hours.

[0110] (3) HER neutral medium performance test The three-electrode system consists of an electrode clip (working electrode), a silver / silver chloride electrode (reference electrode), a carbon rod (counter electrode), and an electrolyte. The potential conversion formula between the silver / silver chloride electrode and the reversible hydrogen electrode (RHE) is: E RHE =E Ag / AgCl +0.059pH +0.2046.

[0111] A three-electrode system was installed, using 1.0 M phosphate-buffered saline (PBS) as the electrolyte. Co-MoC / Mo2C, Co-Mo2C, and Co-MoO3 samples were cut into 0.5 cm × 1.5 cm pieces. The cut samples were fixed with electrode clips, ensuring that the sample immersion area in the liquid was 0.5 cm × 0.5 cm. Testing then commenced. Cyclic voltammetry (CV) was used to activate the samples at a scan rate of 100 mV·s. -1After the curves basically overlap, the linear sweep voltammetry (LSV) test is started at a rate of 5 mV·s. -1 The LSV curve was obtained by reverse scanning within a potential range of (-0.4) to (-1.1) V. The double-layer capacitance (C...) dl Within the non-Rad-day interval, CV curves were obtained by testing at different scan rates. The scan rate was plotted on the x-axis, and the difference between the median values ​​of the intervals was divided by two to form the y-axis. The resulting slope after fitting is the double-layer capacitance. The test results are as follows: Figure 7 As shown.

[0112] Figure 7 The relevant results and analysis are as follows: like Figure 7 As shown in Figure a, the LSV curves after iR correction show that Co-MoC / Mo2C exhibits excellent catalytic activity at a current density of 10 mA cm⁻¹. -2 and 100mA cm -2 At that time, the overpotentials were as low as 71mV and 240mV, respectively, which are much smaller than the overpotentials of Co-Mo2C (η10=139mV, η100=258mV) and Co-MoO3 (η10=393mV, η100=467mV), solving the problem of low proton concentration and slow kinetics under neutral conditions.

[0113] like Figure 7 As shown in Figure b, the Tafel slope of Co-MoC / Mo2C is 74.2 mV dec. -1 It is lower than Co-Mo2C (109.1 mV dec). -1 ) and Co-MoO3 (120.5mV dec -1 This indicates that the electrocatalytic composite material Co-MoC / Mo2C possesses excellent catalytic kinetics.

[0114] like Figure 7 As shown in Figure c, the charge transfer rate (Rct) of the above samples was further studied by electrochemical impedance spectroscopy (EIS). The impedance value is negatively correlated with the electron transfer rate. The larger the impedance value, the slower the electron transfer rate of the sample. The results show that the Rct of Co-MoC / Mo2C is smaller than that of Co-Mo2C and Co-MoO3, indicating that Co-MoC / Mo2C has the fastest electron transport rate in the HER catalysis process.

[0115] like Figure 7 As shown in Figure d, to further explore the electrochemical activity of different samples, the double-layer capacitance of the samples was tested at different scan rates in the non-Radida potential region. Then, the C0 of the samples was obtained by fitting cyclic voltammetry curves. dlThe Ca value was used to evaluate its electrochemically active surface area (ECSA); the results showed that the Ca of Co-MoC / Mo2C was significantly higher than that of Mo2C. dl The value is as high as 46.92mF cm -2 It is significantly superior to Co-Mo2C (38.67 mF cm⁻¹). -2 ) and Co-MoO3 (37.8mF cm -2 ).

[0116] In summary, this invention provides an electrocatalytic composite material based on cobalt single-atom-controlled molybdenum carbide phase transition, its preparation method, and its application, aiming to develop non-noble metal catalytic materials with atomically precise structures. This invention is the first to propose using cobalt single atoms as an inducer to control the phase transition from the α phase (MoC) to the β phase (Mo2C) of molybdenum-based carbides, thereby achieving catalytic water electrolysis activity. This invention employs a hydrothermal synthesis method and a high-temperature carbonization method to anchor cobalt single atoms onto the carbides. Through this cobalt single-atom anchoring strategy, the phase structure of the transition metal carbides (MoC / Mo2C) is precisely controlled, optimizing their electronic structure and catalytic performance. This enables water electrolysis applications across the entire pH range under high operating current conditions, offering the advantage of adaptability to various electrolysis scenarios.

[0117] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing an electrocatalytic composite material based on cobalt single-atom-controlled molybdenum carbide phase transition, characterized in that, Including the following steps: A cobalt source, a molybdenum source, and a surfactant are dispersed in water, and the pH is adjusted to acidity to obtain a reaction solution. The substrate was placed in the reaction solution and reacted at 150-250°C for 4-8 hours to obtain the precursor. The precursor and carbon source were placed in an inert atmosphere and heated to 800-1000℃ at a heating rate of 3-7℃ / min and held for 1-3 hours to obtain an electrocatalytic composite material. In the reaction solution, the molar ratio of molybdenum to cobalt is 1:(0.05~0.12). The amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.01~0.03).

2. The method for preparing the electrocatalytic composite material according to claim 1, characterized in that, The cobalt source is selected from one or more of cobalt chloride, cobalt nitrate, cobalt acetate, cobalt sulfate, and cobalt oxalate; The molybdenum source is selected from one or more of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and ammonium phosphomolybdate.

3. The method for preparing the electrocatalytic composite material according to claim 1, characterized in that, In the reaction solution, the molar ratio of molybdenum to the surfactant is 1:(0.01~1). The surfactant is selected from one or more of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfate.

4. The method for preparing the electrocatalytic composite material according to claim 1, characterized in that, The amount of carbon source is added according to the molar amount of molybdenum in the reaction solution, and the molar ratio of molybdenum to carbon source is 1:(0.015~0.02). The carbon source is selected from one or more of dicyandiamide, melamine, and cyanamide.

5. The method for preparing the electrocatalytic composite material according to claim 1, characterized in that, The acidity refers to a pH of 1 to 2.

6. The method for preparing the electrocatalytic composite material according to claim 1, characterized in that, The substrate is carbon cloth.

7. The method for preparing the electrocatalytic composite material according to claim 6, characterized in that, The carbon cloth is pretreated; The preprocessing includes the following steps: The carbon was placed in nitric acid and reacted at 130-150°C for 8-12 hours. After removal, it was washed.

8. The method for preparing the electrocatalytic composite material according to claim 1, characterized in that, The inert atmosphere is nitrogen.

9. An electrocatalytic composite material based on cobalt single-atom modulation of molybdenum carbide phase transition, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the electrocatalytic composite material of claim 9 in the hydrogen evolution reaction.

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