Confined Co3Mo3N-Co heterostructure composite materials, their preparation methods and applications

Abstract

The application belongs to the field of electrocatalytic hydrogen evolution, and provides a confined Co3Mo3N-Co heterostructure composite material, a preparation method and application thereof. A mixed solution of dicyandiamide, a divalent cobalt salt and a hexavalent molybdenum salt is evaporated to dryness to obtain a CoMo-containing precursor powder; the CoMo-containing precursor powder is subjected to high-temperature pyrolysis treatment under an inert gas atmosphere, so that monodisperse confined structures are formed, and the confined Co3Mo3N-Co heterostructure composite material is obtained. The confined Co3Mo3N-Co heterostructure composite material can be used as a water electrolysis catalyst for electrocatalytic hydrogen evolution reaction.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic hydrogen evolution, specifically relating to hydrogen evolution electrocatalytic composite materials, their preparation methods, and applications. Background Technology

[0002] Water electrolysis is considered one of the most efficient ways to obtain clean and sustainable hydrogen energy, which holds the promise of replacing the rapidly consumed fossil fuels. However, the hydrogen evolution reaction (HER) in alkaline electrolytes is kineticly slow and has a high energy barrier due to interference from hydroxyl groups and complex water adsorption / dissociation processes, requiring a significant additional energy input. Currently, platinum-based catalysts are the most efficient HER catalysts, but their scarcity, high cost, and poor chemical stability severely hinder the practical application of water electrolysis technology. Against this backdrop, exploring efficient and low-cost alkaline HER electrocatalysts is of great significance for the large-scale commercial application of water electrolysis for hydrogen production.

[0003] Among inexpensive transition metal-based materials, transition metal alloy nitrides (such as Co3Mo3N) have gradually attracted researchers' attention in the field of electrocatalytic hydrogen production due to their unique platinum-like surface electronic structure. However, how to significantly reduce the energy barrier and improve the alkaline HER kinetics of transition metal alloy nitride-based catalysts still faces huge challenges. Summary of the Invention

[0004] In view of this, the present invention provides confined Co3Mo3N-Co heterostructure composite materials, their preparation methods and applications, thereby solving at least one problem existing in the prior art.

[0005] The method for preparing confined Co3Mo3N-Co heterostructure composite material provided by the present invention includes the following steps: Divalent cobalt salt and hexavalent molybdenum salt were added to a dicyandiamide solution to form a mixed solution, which was then evaporated to dryness and ground to form a CoMo-containing powder precursor. The CoMo-containing powder precursor was subjected to high-temperature annealing in an inert gas atmosphere to obtain the confined Co3Mo3N-Co heterostructure composite material.

[0006] Interface engineering between Co3Mo3N and metallic Co can increase the electron density and active sites of Co3Mo3N, thereby balancing the free energy of water dissociation and hydrogen adsorption intermediates, accelerating HER kinetics, and lowering the reaction energy barrier. The confined support provided by porous nitrogen-doped carbon (PNC) further optimizes the activity of the metal-based component and ensures structural and chemical stability in corrosive alkaline solutions. Therefore, the confined Co3Mo3N-Co heterostructure composite material can significantly improve the activity and stability of transition metal alloy nitride water electrolysis catalysts.

[0007] The above method yields a confined Co3Mo3N-Co heterostructure composite material, meaning that the present invention also provides a confined Co3Mo3N-Co heterostructure composite material obtained by the above method.

[0008] The confined Co3Mo3N-Co heterostructure composite material can be used as a water electrolysis catalyst for the electrocatalytic hydrogen evolution reaction. Therefore, the present invention also provides a water electrolysis catalyst comprising the confined Co3Mo3N-Co heterostructure composite material.

[0009] The technical solutions adopted in the embodiments of the present invention can achieve at least the following beneficial effects: (1) A strategy of synergistic enhancement of the activity of transition metal alloy nitride catalysts by interface engineering and confined structure is proposed. This strategy is simple, easy to operate and highly reproducible. (2) Based on the design of confined Co3Mo3N-Co heterostructure, the electronic structure of each component is effectively adjusted, charge transfer is promoted, and the number and enhancement of active sites are increased; (3) The obtained confined Co3Mo3N-Co heterostructure composite material can reduce the barrier to processes such as water dissociation and hydrogen adsorption / desorption, improve the kinetics, and exhibit excellent alkaline HER performance. (4) This invention combines confined structure and surface / interface engineering techniques to promote the HER process through “internal and external cooperation”, and has broad prospects in the fields of developing efficient, stable and low-cost electrocatalysts and designing sustainable energy systems for practical applications. Attached Figure Description

[0010] Figure 1 This is the XRD pattern of the confined Co3Mo3N-Co heterostructure composite material of Example 1.

[0011] Figure 2 This is the EDX-Mapping diagram of the confined Co3Mo3N-Co heterostructure composite material of Example 1.

[0012] Figure 3 This is a SEM image of the confined Co3Mo3N-Co heterostructure composite material of Example 1.

[0013] Figure 4 This is a TEM image of the confined Co3Mo3N-Co heterostructure composite material of Example 1.

[0014] Figure 5 Linear sweep voltammetric polarization curves of the confined Co3Mo3N-Co heterostructure composite material of Example 2 as an electrocatalyst in 1 MKOH are shown.

[0015] Figure 6 The Tafel curves of the confined Co3Mo3N-Co heterostructure composite material of Example 2 as an electrocatalyst are shown, fitted by linear sweep voltammetry polarization curves.

[0016] Figure 7 The confined Co3Mo3N-Co heterostructure composite material of Example 2 was shown as an electrocatalyst at a constant 10 mA / cm². 2 Chrono-potential curves at current density.

[0017] Figure 8 This is a TEM image of the confined Co3Mo3N-Co heterostructure composite material from Example 2 after stability testing as an electrocatalyst. Detailed Implementation

[0018] The following will provide a clear and complete description of the concept and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully illustrate the purpose, solution and effects of the present invention.

[0019] In specific implementation, the preparation method of the confined Co3Mo3N-Co heterostructure composite material provided by the present invention may include the following steps S1~S2: S1. Divalent cobalt salt and hexavalent molybdenum salt are added to dicyandiamide solution to form a mixed solution, evaporated to dryness, and ground to form a CoMo-containing powder precursor; In step S1, the divalent cobalt salt is selected from cobalt salts such as CoCl2 and CoSO4, and the divalent cobalt salt may contain water of crystallization, such as CoCl2∙6H2O and CoSO4∙7H2O; the hexavalent molybdenum salt is selected from H3[P(Mo3O4)2]... 10 Molybdenum salts such as Na₂MoO₄, and the hexavalent molybdenum salts may contain water of crystallization, for example, H₃[P(Mo₃O₄)₂]₃. 10 )4]· x H2O, Na2MoO4·2H2O. In the mixed solution, the mass concentration of CoCl2∙6H2O can be 2 mg / mL to 3 mg / mL, preferably 2.6 mg / mL; H3[P(Mo3O 10 )4]· x The mass concentration of H2O can be 1 mg / mL to 2 mg / mL, preferably 1.7 mg / mL.

[0020] In step S1, the dicyandiamide solution is an aqueous solution of dicyandiamide, which can be prepared by dicyandiamide and deionized water. In the dicyandiamide solution, the mass concentration of dicyandiamide can be 10 mg / mL to 20 mg / mL, preferably 16.8 mg / mL.

[0021] S2. The CoMo-containing powder precursor is subjected to high-temperature annealing in an inert gas atmosphere to obtain the confined Co3Mo3N-Co heterostructure composite material.

[0022] In step S2, the high-temperature annealing treatment refers to holding the material at 450℃~550℃ for 1.5 h~2.5 h, and then at 750℃~850℃ for 1.5 h~2.5 h; preferably, holding it at 500℃ for 2 h, and then at 800℃ for 2 h. The inert gas can be argon, nitrogen, or other inert gases. In specific operation, the CoMo-containing powder precursor can be spread evenly in a ceramic boat, placed in a tube furnace, and heated from room temperature to the target temperature at a rate of 5℃ / min under a high-purity Ar gas atmosphere.

[0023] According to the preparation method of the confined Co3Mo3N-Co heterostructure composite material provided by the present invention, the confined Co3Mo3N-Co heterostructure composite material can be obtained.

[0024] An ink-like catalyst dispersion, prepared by mixing a confined Co3Mo3N-Co heterostructure composite material, Nafion solution, and ethanol, can be used as a water electrolysis catalyst after drying. For example, the ink-like catalyst dispersion can be coated onto an electrode and dried to prepare an electrocatalyst electrode for electrocatalytic hydrogen evolution reaction.

[0025] The present invention will now be described in detail with reference to specific embodiments.

[0026] Example 1 Confined Co3Mo3N-Co heterostructure composite materials were prepared according to the following procedure: (1) Weigh 1.176 g of dicyandiamide and dissolve it in a beaker containing 70 mL of deionized water; then add 0.1816 g of CoCl2∙6H2O and 0.1161 g of H3[P(Mo3O4)2] 10 )4]· x H2O (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was stirred for 1 h; then, the solution in the beaker was kept stirred and kept open at 75 °C until it was completely evaporated; after cooling to room temperature, it was ground into powder, which is the CoMo-containing powder precursor. (2) The above CoMo-containing powder precursor was spread in a ceramic boat and placed in the middle of a tube furnace. Under a high-purity Ar gas atmosphere, the temperature was increased from room temperature to 500°C at a rate of 5°C / min and held for 2 h. Then, the temperature was increased to 800°C at a rate of 5°C / min and held for 2 h. Finally, the mixture was naturally cooled to obtain a confined Co3Mo3N-Co heterostructure composite material.

[0027] The product was analyzed using X-ray diffraction (XRD), and the results showed that the product contained a crystalline phase. Figure 1 This is the XRD pattern of the confined Co3Mo3N-Co heterostructure composite material of Example 1. Comparison with the standard card confirms that the obtained composite material contains cubic Co3Mo3N and cubic metallic Co. Amorphous porous nitrogen-doped carbon was not detected by the XRD instrument.

[0028] The elemental distribution and composition of the product were determined by energy-dispersive X-ray spectroscopy (EDX-mapping) with a TEM. Figure 2 The image shows the EDX-Mapping of the confined Co3Mo3N-Co heterostructure composite material of Example 1, revealing that elements such as Co and Mo are mainly concentrated in the particulate heterostructure Co3Mo3N-Co region, while C, N and O elements are uniformly distributed on the nitrogen-doped porous carbon that provides confined support.

[0029] The surface, interface morphology, and structure of the product were determined by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 3 The image shown is a SEM image of the confined Co3Mo3N-Co heterostructure composite material of Example 1, which shows that the surface of the material exhibits a rich three-dimensional hierarchical porous structure. Figure 4 This is a TEM image of the confined Co3Mo3N-Co heterostructure composite material of Example 1. Figure 4 As shown in (a), a rich hierarchical porous nitrogen-doped carbon material was observed as a support, which contains a large number of monodisperse particle nanostructures uniformly confined inside. Figure 4 Image (b) (high-resolution TEM image) reveals a continuous lattice interface between the monodisperse confined particulate Co3Mo3N phase and metallic Co. A lattice distance of 2.49 nm (10d) corresponds to the (331) plane of Co3Mo3N, and a lattice distance of 2.09 nm (10d) corresponds to the (111) plane of the metallic Co phase. These structural characterizations demonstrate that a confined Co3Mo3N-Co heterostructure composite material was successfully prepared.

[0030] Example 2 Performance testing of confined Co3Mo3N-Co heterostructure composite material as a catalyst for hydrogen evolution reaction in water electrolysis: (1) Preparation of the working electrode for the electrocatalyst: First, weigh 5 mg of confined Co3Mo3N-Co heterostructure composite powder and add it to a 2 mL centrifuge tube. Then add 40 μl of 960 μL ethanol and 5 wt% Nafion solution, and shake several times. Second, place the centrifuge tube on a suspension foam rack and treat it in an ultrasonic cleaner for more than 30 min to form a relatively uniform ink-like catalyst dispersion. Finally, use a pipette to drop the ink-like catalyst dispersion onto the surface of a 3 mm diameter glassy carbon electrode disk in 5 portions (1.6 μL each time). After air drying to form a film, the electrocatalyst-modified glassy carbon electrode is obtained.

[0031] (2) Electrochemical performance study: Electrochemical performance tests were conducted on a Shanghai Chenhua electrochemical workstation (model CHI760E) using the prepared electrocatalyst working electrode. For the HER test, a 1 mol / L KOH aqueous solution was used as the electrolyte; the three-electrode system was configured as follows: a glassy carbon electrode modified with the prepared electrocatalyst as the working electrode, a graphite rod as the auxiliary electrode, and a saturated calomel electrode (SCE) as the reference electrode. According to the Nernst equation, all potentials tested were converted to reversible hydrogen electrode potentials (…). E RHE ); Subtract 0 V E RHE This is a HER overpotential. η .

[0032] After immersing the three-electrode configuration in the electrolyte and connecting it to the workstation, the following operations were performed: (i) A linear voltammetric scan was conducted at a rate of 2 mV / s to obtain the polarization curve; (ii) Based on the data obtained from the polarization curve (potential)... E RHE and current density j ),Establish E RHE and log|current density( j mA / cm 2 Linear regression between )| can be used to calculate the Tafel slope for the HER process at the electrocatalyst working electrode; (iii) at 10 mA / cm 2 The stability of the working electrode of the prepared electrocatalyst was obtained by chronopotential testing at constant current density.

[0033] Figure 5 The linear sweep voltammetric polarization curve of the confined Co3Mo3N-Co heterostructure composite material used in Example 2 as an electrocatalyst in 1 M KOH is shown. The test results indicate that the confined Co3Mo3N-Co heterostructure composite material exhibits excellent alkaline HER electrocatalytic activity, producing 10 mA / cm².2 The reference current density (comparable to the current density produced by a solar device with an efficiency of 12.3%) requires only 67 mV overpotential.

[0034] Figure 6 The figure shows the Tafel curve obtained by fitting the linear sweep voltammetric polarization curve based on the confined Co3Mo3N-Co heterostructure composite material of Example 2 as an electrocatalyst. The figure shows that the Tafel slope of the confined Co3Mo3N-Co heterostructure composite material is only 43.1 mV / dec, and its ultra-low value means that the composite material has ultrafast alkaline hydrogen evolution reaction kinetics.

[0035] Figure 7 The confined Co3Mo3N-Co heterostructure composite material of Example 2 was used as an electrocatalyst at a constant 10 mA / cm². 2 Chronopotential curves at current density. Tests show that the composite material exhibits excellent stability, with no significant increase in potential during 20 hours of electrocatalysis.

[0036] Figure 8 This is a TEM image of the confined Co3Mo3N-Co heterostructure composite material from Example 2 after stability testing as an electrocatalyst. The image shows that the morphology of the confined Co3Mo3N-Co heterostructure composite material remained consistent with its initial morphology after the stability test, indicating that this composite material exhibits good structural and performance stability as a HER catalyst for water electrolysis.

[0037] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. Any embodiment that achieves the technical effects of the present invention using the same means should fall within the protection scope of the present invention. Within the protection scope of the present invention, various modifications and variations can be made to the technical solutions and / or implementation methods.

Claims

1. A method for preparing confined Co3Mo3N-Co heterostructure composite materials, comprising the following steps: A mixed solution of divalent cobalt salt and molybdenum source was formed by adding it to a dicyandiamide solution, which was then evaporated to dryness and ground to form a CoMo-containing powder precursor. The CoMo-containing powder precursor was subjected to high-temperature annealing in an inert gas atmosphere to obtain the confined Co3Mo3N-Co heterostructure composite material. The high-temperature annealing treatment refers to first holding the temperature at 450℃~550℃ for 1.5 h~2.5 h, and then holding it at 750℃~850℃ for 1.5 h~2.5 h. The divalent cobalt salt is selected from CoCl2, CoSO4, and CoCl2. 6H2O, CoSO4 7H2O; the molybdenum source is selected from H3[P(Mo3O] ] 10 )4], Na2MoO4, H3[P(Mo3O 10 )4]· x H2O, Na2MoO4·2H2O.

2. The method according to claim 1, characterized in that, In the mixed solution, the mass concentration of dicyandiamide is 10 mg / mL to 20 mg / mL, and the CoCl2 content is... The mass concentration of 6H2O is 2 mg / mL~3 mg / mL, H3[P(Mo3O) 10 )4]· x The mass concentration of H2O is 1 mg / mL to 2 mg / mL.

3. The method according to claim 2, characterized in that, In the mixed solution, the mass concentration of dicyandiamide was 16.8 mg / mL, and the CoCl2 content was... The mass concentration of 6H2O is 2.6 mg / mL, H3[P(Mo3O)] 10 )4]· x The mass concentration of H2O is 1.7 mg / mL.

4. The method according to claim 1, characterized in that, The high-temperature annealing treatment refers to first holding the temperature at 500°C for 2 hours, and then holding it at 800°C for 2 hours.

5. The confined Co3Mo3N-Co heterostructure composite material obtained by the method according to any one of claims 1 to 4.

6. The application of the confined Co3Mo3N-Co heterostructure composite material according to claim 5 in the electrocatalytic hydrogen evolution reaction.

7. A water electrolysis catalyst, characterized in that, The water electrolysis catalyst comprises the confined Co3Mo3N-Co heterostructure composite material as described in claim 5.

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