Tungsten / vanadium nitride heterojunction electro-catalytic material and preparation method thereof

Abstract

The invention discloses a tungsten / vanadium nitride heterojunction electro-catalytic material and a preparation method thereof.The preparation method comprises the steps that vanadium chloride, tungsten chloride and oxalic acid are dissolved in ethyl alcohol, the molar ratio of vanadium chloride to tungsten chloride is (0.5-3): (1-3), and a mixed solution is obtained; adjusting the pH value of the mixed solution to 1-4, carrying out hydrothermal treatment to obtain a reaction solution, washing a product in the reaction solution, and drying to obtain powder; the tungsten / vanadium nitride heterojunction electro-catalysis material is obtained by calcining the powder and a carbon source in an argon atmosphere according to the proportion of (200-600) mg: (0.5-1.2) mol, and the tungsten / vanadium nitride heterojunction electro-catalysis material is simple and feasible, low in raw material cost, green and pollution-free, and high in electro-catalysis hydrogen evolution activity and stability in an alkaline environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen evolution by electrolysis of water, and in particular relates to a tungsten / vanadium nitride heterojunction electrocatalytic material and a preparation method thereof. Background Art

[0002] To address the world's growing energy demand and its impact on global warming, the search for renewable energy alternatives to fossil fuels is urgent. Hydrogen, with its high energy density and pollution-free emissions, is considered the most promising next-generation sustainable energy source. Electrocatalytic water splitting (HER) is a green, environmentally friendly, and sustainable new energy technology. Currently, water electrolysis technology is relatively mature and has entered the initial industrialization stage. Compared with other hydrogen production methods, water electrolysis offers the following advantages: 1. Earth's water reserves are abundant and recyclable; 2. The electrolysis process only produces oxygen and hydrogen, without greenhouse gases and secondary environmental pollution; 3. The reaction product is as high as 99.9% pure; 4. The electricity used in the hydrogen production process can be converted from wind power, solar power, or other renewable energy sources. However, the water electrolysis reaction itself has a high reaction barrier, and the hydrogen evolution process requires a large amount of electricity. Therefore, to reduce the cost of water electrolysis hydrogen production and achieve large-scale application, the development of inexpensive and effective catalysts is necessary.

[0003] To date, precious metal catalysts can lower the energy barrier of water electrolysis and promote the HER reaction, but their high cost has hindered their further development. Numerous studies have shown that non-precious metal catalysts, such as phosphides, sulfides, oxides, nitrides, and carbides, are the most promising alternatives to platinum-based catalysts. Compared to precious metal catalysts, they overcome the disadvantages of high cost and poor electrochemical stability. Among them, transition metal nitrides (TMNs) have garnered widespread attention in the field of water electrolysis in recent years due to their excellent acid-base tolerance, unique electronic structure, and properties similar to precious metals. These transition metal nitrides exhibit a combination of metallic, covalent, and ionic properties. The metallic properties contribute to high conductivity, while the covalent bonds impart hardness, brittleness, and improved stress tolerance. During the formation of TMNs, as nitrogen atoms incorporate into the transition metal lattice, the interactions between the metal and nitrogen atoms expand the metal lattice and d-band density, increasing the density of states near the Fermi level, giving them an electronic structure similar to Pt and metal-like electron transport properties, resulting in high conductivity. Vanadium nitride (VN) has attracted much attention in recent years as a classic transition metal nitride electrocatalytic material. VN has both metallic conductivity (resistivity ~10 -6Ω·m) and precious metal-like catalytic activity, and its charge transfer efficiency far exceeds that of most transition metal oxides or sulfides. At the same time, it is acid and alkali resistant, stable in nature, and can work stably in concentrated acid or strong base. However, the catalytic activity of pure VN is still not ideal and cannot reach the catalytic activity of precious metal-based catalysts. The chemical adsorption energy ΔGH* of atomic hydrogen on the catalyst surface is one of the key indicators to measure the quality of HER catalysis. For high-performance HER catalysts, the binding energy between the adsorbed atomic hydrogen and the catalyst surface needs to be in an appropriate range. The MH binding energy of VN is large, which leads to slow kinetics of its desorption process with hydrogen, hindering the overall catalytic process. Therefore, it is necessary to modify pure VN to improve its MH binding energy.

[0004] To improve the catalytic performance of vanadium nitride (VN) to meet the needs of industrial production, researchers usually adopt modification strategies such as heteroatom doping, defect engineering, nanostructure construction, heterostructure design, and multi-metal system construction. Among them, heterostructure design can regulate the electronic state density and adsorption energy at the active site of the hydrogen evolution reaction (HER) of the material due to the electronic interaction between different components at the heterogeneous interface (such as charge transfer and orbital coupling), optimize the adsorption / desorption kinetics of reaction intermediates, significantly improve the intrinsic catalytic activity, and inhibit the oxidation / dissolution of active components at extreme potentials, further improving the stability of the material. It has become one of the important means to improve the electrocatalytic hydrogen evolution performance of VN. For example, the composite of transition metal phosphides and vanadium nitride to form a heterostructure can improve the intrinsic catalytic reaction kinetics and catalytic stability of the material. However, the solid-phase sintering reaction during the preparation process causes severe agglomeration of the material, inhibiting the exposure of the active sites of the material and resulting in poor catalytic performance. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a tungsten / vanadium nitride heterojunction electrocatalytic material and a preparation method thereof, so as to solve the problem that the solid-phase sintering reaction when transition metal phosphide and vanadium nitride are composited leads to severe agglomeration of the material, inhibits the leakage of the material active sites, and leads to poor catalytic performance. The present invention is simple and easy to implement, has low raw material cost, is green and pollution-free, has high electrocatalytic hydrogen evolution activity in an alkaline environment, and has strong stability.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a tungsten / vanadium nitride heterojunction electrocatalytic material comprises the following steps:

[0008] S1, dissolving vanadium chloride, tungsten chloride, and oxalic acid in ethanol, wherein the molar ratio of vanadium chloride to tungsten chloride is (0.5-3):(1-3), to obtain a mixed solution;

[0009] S2, adjusting the pH value of the mixed solution to 1-4 and then performing hydrothermal treatment to obtain a reaction solution, washing the product in the reaction solution and drying it to obtain a powder;

[0010] S3, calcining the powder and the carbon source in an argon atmosphere at a ratio of (200-600) mg: (0.5-1.2) mol to obtain a tungsten / vanadium nitride heterojunction electrocatalytic material.

[0011] Preferably, the ratio of ethanol to vanadium chloride in S1 is (20-100) ml: (0.5-3) mmol.

[0012] Preferably, the concentration of oxalic acid in the mixed solution in S1 is 0.01-0.5 mol / L.

[0013] Preferably, S2 uses 1 mol / L hydrochloric acid to adjust the pH value of the mixed solution to 1-4.

[0014] Preferably, S2 adjusts the pH value of the mixed solution to 1-4, performs ultrasonic treatment for 1-2 hours, and then performs hydrothermal treatment.

[0015] Preferably, the temperature of the hydrothermal treatment in S2 is 140-200° C., and the time is 12-36 h.

[0016] Preferably, in S3, the powder is placed in a porcelain boat and calcined under an inert atmosphere with the carbon source at the air inlet.

[0017] Preferably, the carbon source described in S3 is melamine.

[0018] Preferably, S3 is heated from room temperature at a heating rate of 5-10°C / min, and the calcination treatment is performed at 600-900°C for 1-3 hours.

[0019] A tungsten / vanadium nitride heterojunction electrocatalytic material obtained by any one of the above methods for preparing a tungsten / vanadium nitride heterojunction electrocatalytic material.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The present invention discloses a method for preparing a tungsten / vanadium nitride heterojunction electrocatalytic material. Under acidic conditions with a pH of 1-4, vanadium chloride and tungsten chloride undergo an oxidation reaction. Under the action of oxalic acid, the precipitated powder undergoes oriented growth to form a nanoflower structure of stacked nanosheets, WO3 / V2O5 powder. Subsequently, by adjusting the ratio of the powder to a carbon source, a one-step solid-phase sintering method is used, and the reducing gas generated by the decomposition of the carbon source reacts with the powder to prepare the tungsten / vanadium nitride heterojunction electrocatalytic material. The synthesis strategy of in-situ generation of tungsten / vanadium nitride (W / VN) from a precursor is adopted. While effectively maintaining the micromorphology of the precursor, the agglomeration of the material can be avoided. Tungsten (W) has a high melting point, high conductivity, corrosion resistance, and a unique electronic structure. The combination of VN's ability to accelerate internal electron transfer speed and the high conductivity of W metal can compensate for the shortcomings of VN's semiconductor properties, accelerate the charge transfer rate, enhance the material's internal electron transfer efficiency, and obtain stronger conductivity. At the same time, it has excellent acid-base tolerance and exhibits excellent electrocatalytic hydrogen evolution performance. The W / VN electrocatalytic material has a simple preparation process and easily controllable conditions. Through the synergistic action of the two components, the low d-band center position of VN is adjusted, the Fermi level position is adjusted, and interfacial charge redistribution activates inert sites. This simultaneously lowers the d-band center of VN, optimizes the free energy of the hydrogen evolution reaction, weakens hydrogen adsorption strength, and avoids excessive adsorption of hydrogen atoms by the catalytic material, which makes desorption difficult. This promotes the kinetics of the hydrogen evolution process and further enhances the material's conductivity, resulting in excellent HER performance and catalytic stability. The heterojunction structure, composed of ultrathin nanosheets stacked together to form a multi-level hierarchical 3D nanoflower structure, has a high specific surface area, providing more reactive sites for the HER reaction, further enhancing the binding capacity of reactants during the reaction and promoting the electrocatalytic water splitting reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the X-ray diffraction analysis diagram of the W / VN electrocatalytic material in Example 1.

[0023] Figure 2 Graph showing the electrocatalytic hydrogen evolution performance of VN and Example 1 W / VN electrocatalytic materials.

[0024] Figure 3 This is the SEM image of the W / VN electrocatalytic material in Example 1.

[0025] Figure 4 This is the electrochemically active area (ECSA) diagram of the W / VN electrocatalytic material in Example 1. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0027] The present invention provides a method for preparing a W / VN heterojunction electrocatalytic material, comprising the following steps:

[0028] (1) Weigh 0.5-3 mmol of vanadium chloride (VCl3) and 1-3 mmol of tungsten chloride (WCl6), dissolve them in 20-100 ml of ethanol, then add 0.01-0.5 mol / L oxalic acid (H2C2O4, the concentration after addition), and stir until the mixture is uniform and free of powder. This is referred to as solution A.

[0029] (2) 1 mol / L hydrochloric acid (HCl) was titrated into solution A, and the pH value of the solution was detected using a pH meter until the pH value of solution A was 1-4. Solution A was ultrasonically treated for 1-2 h to obtain solution B.

[0030] (3) Solution B is transferred to a hydrothermal kettle, the filling ratio of which is maintained at 30-70%, the oven temperature is adjusted to 140-200°C, and the reaction time is 12-36h. (An oxidation reaction occurs in the solution under acidic conditions, and the powder precipitated by the reaction grows in an oriented manner under the action of oxalic acid to form a nanoflower structure formed by stacking nanosheets.) After cooling to room temperature, impurity ions are cleaned by centrifugation and freeze drying equipment and dried to obtain powder C (WO3 / V2O5).

[0031] (4) Weigh 200-600 mg of C powder, place it in a small porcelain boat, insert one end of the large porcelain boat, and place 0.5-1.2 mol of carbon source melamine (C3H6N6) at the other end. Transfer it to a tubular furnace so that the end with the carbon source is at the air inlet of the tubular furnace. Calcinate it under argon atmosphere, replacing traditional hazardous gases, and achieve a safer and more environmentally friendly preparation process. Set the calcination temperature to 600-900℃, start heating from room temperature, and heat at a rate of 5-10℃ / min. Keep warm for 1-3 hours and then cool naturally. (During the heating process, the carbon and nitrogen-containing reducing gas generated by the decomposition of the carbon source is carried to the powder C by the argon gas and reacts with C) to obtain the W / VN electrocatalytic material.

[0032] Example 1:

[0033] (1) Weigh 1 mmol of vanadium chloride (VCl3) and 1 mmol of tungsten chloride (WCl6), dissolve them in 100 ml of ethanol, add 0.5 mol / L oxalic acid (H2C2O4), and stir until the solution is uniform and free of powder. This is referred to as solution A.

[0034] (2) 1 mol / L hydrochloric acid (HCl) was titrated into solution A, and the pH value of solution A was tested using a pH meter until the pH value of solution A reached 1. Solution A was ultrasonically treated for 2 h to obtain solution B.

[0035] (3) Solution B was transferred to a hydrothermal reactor, the filling ratio was maintained at 50%, the oven temperature was adjusted to 140°C, the reaction time was 12 h, and after cooling to room temperature, impurity ions were cleaned by centrifugation and freeze drying equipment and dried to obtain powder C.

[0036] (4) Weigh 200 mg of C powder, place it in a small porcelain boat, insert one end of the large porcelain boat, place 0.8 mol of melamine (C3H6N6) at the other end, transfer it to a tubular furnace, so that the end with the carbon source is at the air inlet of the tubular furnace, and calcine it under argon atmosphere. Set the calcination temperature to 900℃, start heating from room temperature, and heat at a rate of 10℃ / min. Keep warm for 3 hours and then cool naturally to obtain W / VN electrocatalytic material.

[0037] Comparative Example 1:

[0038] (1) Weigh 1 mmol of vanadium chloride (VCl3) and dissolve it in 100 ml of ethanol. Add 0.5 mol / L of oxalic acid (H2C2O4) and stir until the solution is uniform and free of powder. This solution is referred to as solution A.

[0039] (2) 1 mol / L hydrochloric acid (HCl) was titrated into solution A, and the pH value of solution A was tested using a pH meter until the pH value of solution A reached 1. Solution A was ultrasonically treated for 2 h to obtain solution B.

[0040] (3) Solution B was transferred to a hydrothermal reactor, the filling ratio was maintained at 50%, the oven temperature was adjusted to 140°C, the reaction time was 12 h, and after cooling to room temperature, impurity ions were cleaned by centrifugation and freeze drying equipment and dried to obtain powder C.

[0041] (4) Weigh 200 mg of C powder, place it in a small porcelain boat, insert one end of the large porcelain boat, and place 0.8 mol of melamine (C3H6N6) at the other end. Transfer it to a tube furnace so that the end with the carbon source is at the air inlet of the tube furnace. Calcinate it under argon atmosphere. Set the calcination temperature to 900°C, start heating from room temperature, and heat at a rate of 10°C / min. Keep warm for 3 hours and then cool naturally to obtain VN.

[0042] like Figure 1 The XRD pattern of the W / VN electrocatalytic material is shown in Figure 2. The peaks at 37.7°, 43.8°, 63.7°, and 76.5° are attributed to the (111), (200), (220), and (311) crystal planes of VN (JCPDS card number 35-0768). The characteristic peaks at 40.264°, 58.274°, and 73.195° correspond to the (110), (200), and (211) crystal planes of W (PDF#04-0806), indicating that the W / VN electrocatalytic material was successfully prepared.

[0043] Figure 2 The figure shows the linear sweep voltammetry (LSV) curve of the W / VN electrocatalytic material measured in a traditional three-electrode system, using a 1M KOH alkaline electrolyte system. To accurately evaluate the material's intrinsic catalytic performance, the experimental data has been 85% IR-compensated to eliminate the influence of the solution's ohmic impedance. The test results show that the material exhibits excellent catalytic activity in the hydrogen evolution reaction (HER), achieving a 10 mA cm-2 overpotential of only 123 mV. -2 The benchmark current density is significantly improved compared to the 437mV of pure phase vanadium nitride.

[0044] Figure 3 This is the SEM image of the W / VN electrocatalytic material. It can be seen from the figure that the W / VN electrocatalytic material is composed of a nanoflower-like structure formed by stacking nanosheets. This three-dimensional nanostructure greatly increases the specific surface area of the sample, which promotes the kinetics of the electrocatalytic water splitting hydrogen release process.

[0045] Figure 4 This is the electrochemically active area (ECSA) diagram of the W / VN material obtained from a cyclic voltammetry test in the non-Faraday current region with a scan rate of 10-120 mV / s. The figure shows that the material has a large ECSA area, indicating that W / VN has more active sites and thus has good catalytic activity.

[0046] Example 2:

[0047] (1) Weigh 3 mmol of vanadium chloride (VCl3) and 1 mmol of tungsten chloride (WCl6), dissolve them in 20 ml of ethanol, add 0.05 mol / L of oxalic acid (H2C2O4), and stir until the solution is uniform and free of powder. This is referred to as solution A.

[0048] (2) 1 mol / L hydrochloric acid (HCl) solution was titrated into solution A, and the pH value of solution A was tested using a pH meter until the pH value of solution A reached 2. Solution A was ultrasonically treated for 2 h to obtain solution B.

[0049] (3) Solution B was transferred to a hydrothermal kettle, the filling ratio was maintained at 50%, the oven temperature was adjusted to 180°C, the reaction time was 12 h, and after cooling to room temperature, impurity ions were cleaned by centrifugation and freeze drying equipment and dried to obtain powder C.

[0050] (4) Weigh 300 mg of C powder, place it in a small porcelain boat, insert one end of the large porcelain boat, place 1 mol of melamine (C3H6N6) at the other end, transfer it to a tubular furnace, so that the end with the carbon source is at the air inlet of the tubular furnace, and calcine it under argon atmosphere. Set the calcination temperature to 900℃, start heating from room temperature, and heat at a rate of 10℃ / min. Keep warm for 2 hours and then cool naturally to obtain W / VN electrocatalytic material.

[0051] Example 3:

[0052] (1) Weigh 2 mmol of vanadium chloride (VCl3) and 3 mmol of tungsten chloride (WCl6), dissolve them in 80 ml of ethanol, add 0.3 mol / L oxalic acid (H2C2O4), and stir until the solution is uniform and free of powder. This is referred to as solution A.

[0053] (2) 1 mol / L hydrochloric acid (HCl) solution was titrated into solution A, and the pH value of solution A was tested using a pH meter until the pH value of solution A reached 1. Solution A was ultrasonically treated for 1 h to obtain solution B.

[0054] (3) Solution B was transferred to a hydrothermal reactor, the filling ratio was maintained at 70%, the oven temperature was adjusted to 200°C, the reaction time was 36 hours, and after cooling to room temperature, impurity ions were cleaned by centrifugation and freeze drying equipment and dried to obtain powder C.

[0055] (4) Weigh 400 mg of C powder, place it in a small porcelain boat, insert one end of the large porcelain boat, place 1 mol of melamine (C3H6N6) at the other end, transfer it to a tube furnace, so that the end with the carbon source is at the air inlet of the tube furnace, and calcine it under argon atmosphere. Set the calcination temperature to 800℃, start heating from room temperature, and heat at a rate of 10℃ / min. Keep warm for 2 hours and then cool naturally to obtain W / VN electrocatalytic material.

Claims

1. A method for preparing a tungsten / vanadium nitride heterojunction electrocatalytic material, characterized in that: The steps include: S1, dissolving vanadium chloride, tungsten chloride, and oxalic acid in ethanol, wherein the molar ratio of vanadium chloride to tungsten chloride is (0.5-3):(1-3), to obtain a mixed solution; S2, adjusting the pH value of the mixed solution to 1-4 and then performing hydrothermal treatment to obtain a reaction solution, washing the product in the reaction solution and drying it to obtain a powder; S3, calcining the powder and the carbon source in an oxygen-free environment at a ratio of (200-600) mg: (0.5-1.2) mol to obtain a tungsten / vanadium nitride heterojunction electrocatalytic material.

2. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: The ratio of ethanol to vanadium chloride in S1 is (20-100) ml: (0.5-3) mmol.

3. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: The concentration of oxalic acid in the mixed solution S1 is 0.01-0.5 mol / L.

4. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: S2 uses 1 mol / L hydrochloric acid to adjust the pH value of the mixture to 1-4.

5. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: S2 adjusts the pH value of the mixed solution to 1-4, performs ultrasonic treatment for 1-2 hours, and then performs hydrothermal treatment.

6. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: The temperature of the hydrothermal treatment in S2 is 140-200°C and the time is 12-36h.

7. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: S3 places the powder in a porcelain boat and calcines it under an inert atmosphere with the carbon source at the air inlet.

8. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: The carbon source described in S3 is melamine.

9. The method for preparing the tungsten / vanadium nitride heterojunction electrocatalytic material according to claim 1, characterized in that: S3 starts heating from room temperature at a heating rate of 5-10°C / min, and calcination is performed at 600-900°C for 1-3h.

10. A tungsten / vanadium nitride heterojunction electrocatalytic material obtained by the preparation method of a tungsten / vanadium nitride heterojunction electrocatalytic material according to any one of claims 1 to 9.

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