A plasma-activated molybdenum-containing nickel-based metal-organic framework hydrogen evolution electrode material and a preparation method thereof

Abstract

The application discloses a kind of plasma-activated molybdenum-containing nickel-based metal organic framework hydrogen evolution electrode materials and preparation method thereof, it is to electrolytic water catalytic hydrogen evolution technical field, it is with nickel foam as substrate, molybdenum-based polyacid solidified nickel-based metal organic framework nanosheet array is in situ grown on it, then it is obtained after plasma activation treatment;The gas used in the plasma activation treatment is hydrogen or nitrogen or the mixed gas of both.The molybdenum-based polyacid is implanted in the in situ growth process of nickel-based metal organic framework, then after the plasma activation of the mixed gas of hydrogen and nitrogen, metal nickel / nickel nitride / nickel-molybdenum alloy / nickel-based metal organic framework heterostructure electrocatalyst is constructed, and it is applied to electrolytic water hydrogen evolution, and has good HER catalytic activity and stability.

Description

Technical Field

[0001] This invention relates to the field of hydrogen evolution technology in water electrolysis catalysis, and particularly to a plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material and its preparation method. Background Technology

[0002] To meet the demands of societal development, global energy resources are being rapidly depleted, leading to a massive increase in carbon dioxide emissions and a severe energy and environmental crisis. The application of new energy sources is therefore imperative. Hydrogen energy is a well-known clean and ideal energy source, and utilizing renewable energy sources, such as solar or wind power generation, to produce hydrogen is of paramount importance to reducing current societal pressures. Hydrogen production through water electrolysis heavily relies on highly efficient catalysts to accelerate reaction kinetics. Currently, the most effective HER catalysts are precious metals (such as Pt). However, precious metal-based electrocatalysts are expensive and scarce. Finding inexpensive, highly active, and stable non-precious metal-based HER electrocatalysts to replace precious metal-based catalysts is urgently needed.

[0003] In recent years, metal-organic frameworks (MOFs) have been explored by researchers for their large specific surface area, tunable pore size, easily modifiable structure, and abundant active sites, serving as catalytic electrode materials in water electrolysis. However, nickel-based metal-organic frameworks (Ni MOFs), for example, commonly used in OER reactions as HER electrocatalysts, suffer from poor stability and low HER activity. Current methods for improving Ni MOF electrocatalysts include introducing phosphorus or sulfur sources to modify Ni MOFs, or using MOF-based materials as sacrificial templates to derive high-performance electrocatalysts to enhance their HER performance. However, these methods often produce toxic byproducts or require high reaction temperatures and long reaction times. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material and its preparation method. The electrode material has excellent HER catalytic activity and stability.

[0005] The present invention proposes a plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material, which is obtained by growing a nickel-based metal-organic framework nanosheet array loaded with molybdenum-based polyacids in situ on nickel foam as a substrate, and then performing plasma activation treatment; the gas used in the plasma activation treatment is hydrogen or nitrogen or a mixture of both.

[0006] This invention also proposes a method for preparing the above-mentioned plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material, comprising the following steps:

[0007] S1. Select a suitable size of nickel foam and clean it thoroughly;

[0008] S2. Dissolve nickel salt, molybdenum-based polyacid, and terephthalic acid in a mixed solvent to obtain a mixed solution; the mixed solvent is composed of N,N-dimethylformamide, ethanol, and deionized water, and stir.

[0009] S3. Immerse the nickel foam in the mixed solution of S2, seal, heat, keep the reaction at the temperature, cool and take out the nickel foam, clean it, and you will get the nickel-based metal-organic framework nanosheet array Ni MOF / POM with molybdenum-based polyacids grown in situ on the nickel foam substrate.

[0010] S4. Place the nickel foam from S3 into the reaction chamber of a plasma-enhanced chemical vapor deposition apparatus, and introduce an activation gas for plasma activation treatment. The activation gas is hydrogen, nitrogen, or a mixture of both, thus obtaining plasma-activated P-Ni MOF / POM.

[0011] Preferably, in step S1, the mixture is ultrasonically cleaned sequentially with anhydrous ethanol and acetone, then ultrasonically cleaned with 2-3 mol / L hydrochloric acid, and finally rinsed with deionized water and anhydrous ethanol and dried.

[0012] Preferably, in S2, the nickel salt is selected from nickel chloride hexahydrate; and the molybdenum-based polyacid is ammonium molybdate.

[0013] Preferably, in S2, the molar ratio of nickel salt, molybdenum polyacid, and terephthalic acid is 10:0.5-1.5:10-12; and the volume ratio of N,N-dimethylformamide, ethanol, and deionized water in the mixed solvent is 14:1-2:1-2.

[0014] Preferably, in S2, the temperature is raised to 120-140℃ and the reaction is maintained for 10-14 hours.

[0015] Preferably, in S3, the volume ratio of hydrogen to nitrogen in the mixed gas is 1:9.

[0016] Preferably, in S3, the conditions for plasma activation treatment are: plasma power of 400W and activation time of 20min.

[0017] This invention also proposes the application of the above-mentioned plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material in electrocatalytic hydrogen evolution.

[0018] Preferably, it is used in the electrocatalytic alkaline electrolysis of water to produce hydrogen.

[0019] This invention implants molybdenum-based polyacids (POMs) into nickel-based metal-organic frameworks (Ni MOFs). During the in-situ growth of Ni MOFs, the POMs enter the pore structure of the MOFs, resulting in a Ni MOF / POM nanosheet array immobilized with molybdenum-based polyacids. After plasma activation using a hydrogen and nitrogen mixer, active species for HER catalysis are generated in a nickel / nickel nitride / nickel-molybdenum alloy. For Ni MOFs, this enhances their conductivity and provides more active species, thereby improving the HER performance of the electrocatalyst. This invention utilizes low-temperature plasma technology to activate the HER electrocatalyst, constructing a heterostructure to synergistically improve the HER performance and stability of the nickel-based metal-organic framework.

[0020] Compared with the prior art, the beneficial effects of this application are mainly reflected in the following aspects:

[0021] 1. This invention provides a simple, efficient and environmentally friendly method for preparing molybdenum-containing metal-organic framework HER catalysts.

[0022] 2. The P-Ni MOF / POM NSAs hydrogen evolution catalyst of the present invention exhibits high hydrogen evolution activity at a current density of 10 mA·cm⁻¹. -2 At this time, only a low hydrogen evolution overpotential of 35mV is required; when the current density is greater than 100mA·cm -2 Its activity even surpasses that of Pt / C catalysts.

[0023] 3. The P-Ni MOF / POM NSAs hydrogen evolution catalyst of the present invention not only has good stability, but also has fast reaction kinetics.

[0024] The P-Ni MOF / POM NSAs prepared by this invention have more active species, a faster charge transfer process, more catalytic active sites, and good performance in water electrolysis and hydrogen evolution. At high current densities, they are comparable to the benchmark Pt / C catalyst and can be applied in the field of electrocatalytic hydrogen evolution. Attached Figure Description

[0025] Figure 1 The X-ray diffraction pattern of P-Ni MOF / POM NSAs prepared in Example 1 of this invention;

[0026] Figure 2 The images shown are scanning electron microscope (SEM) images of the P-Ni MOF / POM NSAs prepared in Example 1 of this invention; where (a) and (b) are low-resolution SEM images, and (c) is a high-resolution SEM image.

[0027] Figure 3The elemental mapping diagram (a) and infrared spectrum (b) of the P-Ni MOF / POM NSAs prepared in Example 1 of this invention are shown.

[0028] Figure 4 X-ray photoelectron spectra of the materials prepared in Example 1 and Comparative Examples 1-3 of this invention; wherein, Ni 2p(a), Mo 3d(b), N 1s(c), C 1s(d) and O 1s(e);

[0029] Figure 5 The LSV curves and corresponding Tafel slopes of the materials prepared in Example 1 and Comparative Examples 1-3 of this invention;

[0030] Figure 6 The LSV curves and corresponding Tafel slopes of the materials prepared in Examples 1-3 of this invention;

[0031] Figure 7 The LSV curves and corresponding Tafel slopes of the materials prepared in Examples 1 and 4-5 are shown.

[0032] Figure 8 Cyclic voltammetry curves and corresponding ECSA and EIS of the materials prepared for Examples 1 and Comparative Examples 1-3 of this invention

[0033] Figure 9 Normalized LSV curves and TOF plots of the materials prepared in Example 1 and Comparative Example 2 of this invention;

[0034] Figure 10 This is a stability diagram of the material prepared in Example 1 of the present invention. Detailed Implementation

[0035] The technical solution of the present invention will now be described in detail through specific embodiments.

[0036] Example 1

[0037] A plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material is prepared as follows:

[0038] (1) Clean a piece of nickel foam (3cm×3cm) with ethanol and acetone using ultrasonic cleaning, clean it with 2M HCl for 15min to remove the surface oxide layer, rinse it with deionized water and anhydrous ethanol respectively, and finally dry it in an oven at 70℃.

[0039] (2) Dissolve 1 mmol nickel chloride hexahydrate, 1 mmol terephthalic acid, and 0.1 mmol ammonium molybdate in 35 mL N,N-dimethylformamide, 2.5 mL ethanol, and 2.5 mL deionized water, and stir continuously. Then transfer to a 100 mL polytetrafluoroethylene liner.

[0040] (3) Immerse the nickel foam treated in step (1) into the solution in step (2), and protect the upper deck with polytetrafluoroethylene tape. Then seal the autoclave and keep it at 125°C for 12 hours, and then let it cool naturally.

[0041] (4) Take out the nickel foam after the reaction in step (3), and rinse it carefully several times with deionized water and anhydrous ethanol under ultrasonic assistance to obtain Ni MOF / POM NSAs.

[0042] (5) Place the Ni MOF / POM-coated nickel foam obtained in step (4) into the reaction chamber of a plasma-enhanced chemical vapor deposition (PECVD) apparatus, introduce gas (H2 / N2 = 1:9), set the plasma power to 400W, and the activation time to 20min. This yields plasma-activated molybdenum-containing nickel-based metal-organic framework nickel foam, i.e., P-Ni MOF / POM NSAs.

[0043] Example 2

[0044] Compared with Example 1, the only difference is that the gas used for ion activation in step (5) is pure hydrogen gas, while the other operations and parameters are the same.

[0045] Example 3

[0046] Compared with Example 1, the only difference is that the gas used for plasma activation in step (5) is pure nitrogen, while the rest of the operations and parameters are the same.

[0047] Example 4

[0048] Compared with Example 1, the only difference is that the amount of ammonium molybdate used in step (5) is 0.05 mol. All other operations and parameters are the same, and plasma-activated molybdenum-containing nickel-based metal-organic framework foam nickel, namely P-Ni MOF / POM NSAs, is obtained.

[0049] Example 5

[0050] Compared with Example 1, the only difference is that the amount of ammonium molybdate used in step (5) is 0.15 mol. All other operations and parameters are the same, and plasma-activated molybdenum-containing nickel-based metal-organic framework foam nickel, namely P-Ni MOF / POM NSAs, is obtained.

[0051] Comparative Example 1

[0052] Compared with Example 1, the only difference is that step (5) is not included. All other operations and parameters are the same, and unplasm-activated nickel-based metal-organic framework nanosheet arrays Ni MOF / POM NSAs are obtained.

[0053] Comparative Example 2

[0054] Compared with Example 1, the only difference is that ammonium molybdate is not contained in step (2), while the other operations and parameters are the same, resulting in molybdenum-free plasma-activated nickel-based metal-organic framework nanosheet arrays P-Ni MOF NSAs.

[0055] Comparative Example 3

[0056] Compared with Example 1, the only difference is that step (2) does not contain ammonium molybdate and step (5) is not included. All other operations and parameters are the same, resulting in a nickel-based metal-organic framework nanosheet array Ni MOFNSAs that is free of molybdenum and not plasma activated.

[0057] The materials prepared in Examples 1-5 and Comparative Examples 1-3 of this invention were characterized and their performance was tested.

[0058] I. Structural Characterization

[0059] 1. XRD characterization

[0060] Observe the XRD patterns of P-Ni MOF / POM NSAs ( Figure 1 The presence of characteristic peaks for Ni, Ni3N, and NiMo4 indicates that Mo has been successfully introduced into Ni MOFs.

[0061] 2. SEM characterization

[0062] Figure 2 a and Figure 2 The low-resolution scanning electron microscope image of b shows the structure of P-Ni MOF / POM NSAs, which can be seen from... Figure 2 The high-resolution scanning electron microscope image of c shows P-Ni MOF / POMP-Ni particles attached to the nickel foam.

[0063] 3. Characterization using elemental mapping and infrared spectra

[0064] Element Mapping Figure 3 a indicates the presence of Ni, Mo, N, and O elements in P-Ni MOF / POM NSAs, and their uniform distribution within the nanosheet array, as shown by the infrared spectrum. Figure 3 b indicates the presence of C=O, -OH, Mo-O, and other groups on P-Ni MOF / POM NSAs.

[0065] 4. XPS characterization

[0066] XPS measurements were further employed to investigate the surface composition and oxidation state of P-Ni MOF / POM NSAs. Comparison of Ni 2p XPS values ​​for Ni MOF / POM NSAs and Ni MOF NSAs before and after plasma activation revealed that, due to the reducing properties of H2 plasma, new characteristic peaks at binding energies of 870 eV and 851.9 eV corresponded to metallic Ni, while the newly appearing characteristic peak at 853.8 eV indicated that Ni... + The formation of molybdenum. Meanwhile, multivalent Mo ions appeared in the Ni MOF / POM NSAs after isotropic activation in Mo 3dXPS, indicating that +6 molybdenum was reduced. Figure 4 The presence of an N-Ni bond at 397.5 eV in cN 1s XPS confirms the formation of Ni3N, and the characteristic peak at 395 eV belongs to Ni-Mo-N, indicating the presence of a nickel-molybdenum alloy. In C 1s XPS, the characteristic peak of the O=C-OH carboxyl group at 288.5 eV corresponds to the CO group on the carboxyl group at 286.3 eV, and the peak at 284.6 eV corresponds to the CC group on the benzene ring. The characteristic peak at 533.5 eV in O1s XPS indicates the presence of water molecules, and the oxygen anion signal at 529.2 eV may be due to the partial oxidation of Ni to NiO upon exposure to air; the peak at 832 eV corresponds to the carbon-oxygen bond in the carboxyl group in C1s XPS.

[0067] II. Electrochemical Performance Testing

[0068] 1. HER activity in 1.0 mol / L KOH electrolyte

[0069] The HER activity of the prepared electrode material in 1 mol / L KOH electrolyte was evaluated in a standard three-electrode system at room temperature (25 °C). Figure 5 As shown in figure a, Ni MOF NSAs and Ni MOF / POM NSAs exhibit poor HER activity. After plasma activation, the HER activity of P-Ni MOF NSAs and P-Ni MOF / POM NSAs is significantly improved. Among them, the catalytic activity of P-Ni MOF / POM NSAs is superior to that of P-Ni MOF NSAs, demonstrating the important role of adding POMs. (The figure is incomplete in the original text.) -2 At this time, P-NiMOF / POM NSAs only require an overpotential of 35mV. At overpotentials greater than 100mA / cm... -2 Under the given current density conditions, P-Ni MOF / POM NSAs even exhibited better HER activity than Pt / C catalysts. To evaluate the catalytic kinetics of the electrocatalysts, the Tafel slope was calculated (…). Figure 5b). The Tafel slopes of Ni MOF NSAs, Ni MOF / POM NSAs, P-Ni MOF NSAs, P-Ni MOF / POM NSAs, and Pt / C are 93.4, 95.8, 93.9, 52.5, and 34.1 mV dec, respectively. -1 The Tafel slope of P-Ni MOF / POM NSAs is lower than that of other electrocatalysts, indicating that they have better HER kinetic performance.

[0070] 2. Effects of different plasma activation gases and different concentrations of ammonium molybdate

[0071] Compare the LSV curves and corresponding Tafel slopes of plasma-activated Ni MOF / POM NSAs under different atmospheres. Figure 6 LSV curves and corresponding Tafel slopes for H2 / N2 plasma activation with different concentrations of ammonium molybdate added. Figure 7 This indicates that H2 / N2 plasma activation and each component play an important role in enhancing HER activity.

[0072] 3. HER charge transfer characteristics

[0073] Figure 8 ad represents the CV curves at cycles 20, 40, 60, 80, and 100 for P-Ni MOF / POM NSAs, Ni MOF / POM NSAs, P-Ni MOF NSAs, and Ni MOFNSAs, respectively. (The last sentence appears to be incomplete and possibly refers to a different context.) Figure 8 As can be seen from e, the Cdl value of P-Ni MOF / POM NSAs is 131.5 mF cm⁻¹. -2 Much larger than Ni MOF NSAs (1.21 mF cm⁻¹) -2 Ni MOF / POM NSAs (1.61mF cm) -2 ) and P-NiMOF NSAs (74.3m F cm -2 This indicates that P-Ni MOF / POM NSAs possess more HER catalytic active sites. The charge transfer characteristics during the HER process were investigated using EIS. The results show that P-Ni MOF / POM NSAs exhibit a smaller charge transfer resistance, significantly lower than that of Ni MOF NSAs, Ni MOF / POM NSAs, and P-Ni MOF NSAs. This implies higher conductivity and a faster electron transfer process in P-Ni MOF / POM NSAs.

[0074] 4. Intrinsic HER activity in 1.0 mol / L KOH electrolyte

[0075] Normalized LSV test results are as follows Figure 9 As shown in figure a, the intrinsic HER performance of P-Ni MOF / POM NSAs is far superior to that of P-Ni MOF NSAs at a current density of 10 mA / cm². -2 Under these conditions, the catalyst has an overpotential of only 22.3 mV. The conversion frequency (TOF) is used to evaluate the intrinsic activity of the catalyst. Figure 9 As shown in Figure b, the TOF value of P-Ni MOF / POM NSAs is consistently higher than that of P-NiMOF NSAs, further confirming that P-Ni MOF / POM NSAs catalyzes excellent intrinsic HER performance.

[0076] 5. Stability Test

[0077] In stability tests, P-Ni MOF / POM NSAs exhibited long-term stability as shown in the following figures. Figure 10 As shown. P-Ni MOF / POM NSAs exhibit strong electrochemical durability. P-Ni MOF / POM NSAs at a current density of 100 mA / cm² -2 Under certain conditions, it can maintain no significant performance degradation within 120 hours.

[0078] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material, characterized in that, It is obtained by growing a nickel-based metal-organic framework nanosheet array with molybdenum-based polyacids in situ on a nickel foam substrate, followed by plasma activation treatment; the gases used in the plasma activation treatment are hydrogen and nitrogen. The method for preparing the nickel-based metal-organic framework nanosheet array immobilized with molybdenum-based polyacids includes dissolving nickel salt, ammonium molybdate, and terephthalic acid in a mixed solvent to obtain a mixed solution; immersing nickel foam in the mixed solution, sealing, heating, maintaining the temperature for reaction, cooling, removing the nickel foam, and washing to obtain the nickel-based metal-organic framework nanosheet array immobilized with molybdenum-based polyacids grown in situ on the nickel foam substrate.

2. A method for preparing a plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material according to claim 1, characterized in that, Includes the following steps: S1. Select a suitable size of nickel foam and clean it thoroughly; S2. Dissolve nickel salt, ammonium molybdate, and terephthalic acid in a mixed solvent to obtain a mixed solution; the mixed solvent consists of N,N-dimethylformamide, ethanol, and deionized water, and stir. S3. Immerse the nickel foam in the mixed solution of S2, seal, heat, keep the reaction at the temperature, cool and take out the nickel foam, clean it, and you will get the nickel-based metal-organic framework nanosheet array NiMOF / POM with molybdenum-based polyacids grown in situ on the nickel foam substrate. S4. Place the nickel foam from S3 into the reaction chamber of a plasma-enhanced chemical vapor deposition apparatus, and introduce an activation gas for plasma activation treatment. The activation gas is hydrogen and nitrogen, thus obtaining plasma-activated P-Ni MOF / POM.

3. The method as described in claim 2, characterized in that, In S1, the cells are ultrasonically cleaned sequentially with anhydrous ethanol and acetone, then ultrasonically cleaned with 2-3 mol / L hydrochloric acid, and finally rinsed with deionized water and anhydrous ethanol and dried.

4. The method as described in claim 2 or 3, characterized in that, In S2, the nickel salt is selected from nickel chloride hexahydrate; the molybdenum-based polyacid is ammonium molybdate.

5. The method as described in claim 2, characterized in that, In S2, the molar ratio of nickel salt, molybdenum polyacid, and terephthalic acid is 10:0.5-1.5:10-12; the volume ratio of N,N-dimethylformamide, ethanol, and deionized water in the mixed solvent is 14:1-2:1-2.

6. The method as described in claim 2, characterized in that, In S2, the temperature is raised to 120-140 ℃ and the reaction is maintained for 10-14 h.

7. The method as described in claim 2, characterized in that, In S4, the volume ratio of hydrogen to nitrogen in the activation gas is 1:

9.

8. The method as described in claim 2, characterized in that, In S4, the conditions for plasma activation treatment are: plasma power of 400 W and activation time of 20 min.

9. The application of a plasma-activated molybdenum-nickel-based metal-organic framework hydrogen evolution electrode material prepared by the method of any one of claims 1 or 2-8 in electrocatalytic hydrogen evolution.

10. The application as described in claim 9, characterized in that, It is used in the electrocatalytic alkaline electrolysis of water to produce hydrogen.

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