Oxalate-based nickel-iron mof doped carbon nanotube catalytic material, preparation method and application

Abstract

The application discloses a preparation method, a catalytic material and application of an oxalate-based nickel-iron MOF doped carbon nanotube catalytic material. The preparation method comprises the following steps: dispersing nickel nitrate hexahydrate, potassium trioxalate ferrate and carbon nanotubes into a methanol solution, stirring at room temperature after ultrasonic treatment to obtain a mixed solution with precipitates, centrifuging the obtained mixed solution, washing with methanol, and vacuum drying to obtain the oxalate-based nickel-iron MOF doped carbon nanotube catalytic material. The oxalate-based coordination is utilized to synthesize the oxalate-based bridged Ni-Fe bimetallic coordination polymer by one-step synthesis. The oxalate-based oxygen bridge bond participates in the transmission of the synergistic effect between the Ni-Fe bimetals. After the carbon nanotubes are doped, the active sites of the catalytic material are fully exposed, and the Ni-Fe bimetals connected by the oxygen bridge can fully exert the synergistic effect between the two.

Description

Technical Field

[0001] This invention relates to the field of electrochemical hydrogen production technology, and in particular to the preparation method, catalytic material, and application of oxalate-based nickel-iron MOF-doped carbon nanotube catalytic materials. Background Technology

[0002] Electrochemical hydrogen production is considered one of the ideal ways to sustainably obtain clean energy. However, the oxygen evolution reaction (OER) at the anolyte has a large overpotential, slow kinetics, and low efficiency, thus requiring suitable electrocatalysts to accelerate this process. Currently, commercial OER catalysts are mainly based on noble metals such as Ir (iridium), Ru (ruthenium), Rh (rhodium), and their oxides, but their scarcity and high cost hinder their widespread application.

[0003] In current research on non-noble metal OER catalysts, Ni-Fe based materials, especially Ni-Fe layered double hydroxides (NiFe-LDHs), have attracted much attention due to their excellent activity. JMHuo et al. [J. Mater. Chem. A 2022, 10, 1815] synthesized a novel two-dimensional Fe-Ni-LDH nanosheet with a unique structure using a simple method of treating 2D Hoffmann-type Fe-Ni MOFs with NaBH4 solution. This material exhibits a high oxygen evolution overpotential η in 1M KOH. 10 The overpotential is only 238 mV. However, the preparation steps of most Ni-Fe based materials with high OER activity are still relatively complex, requiring specific control over the morphology and micro / nano structure of the materials. This places high demands on synthesis techniques and processes, and is also prone to problems with performance stability and durability. Introducing nanoscale conductive components is one of the effective methods to simplify material preparation and obtain high-efficiency OER activity. In the prior art, M. Gong et al. [J. Am. Chem. Soc. 2013, 135, 8452] prepared multi-walled carbon nanotube (CNT) doped NiFe LDH, which showed an overpotential η in 1 mH₂O. 10 The overpotential is only 250 mV. Furthermore, F. Rong et al. [RSC Adv. 2016, 6, 74536] prepared another nickel-iron-based composite material, NiFe LDH / CNT, by doping CNTs in an alkaline solution. This composite material also exhibited a low overpotential of 278 mV and significantly higher activity than NiFe-LDH without carbon nanotube doping. Y. Liu et al. [ChemCatChem. 2022, 14, 202200453] used NH3 and CO2 from the air to embed carbon nanotubes and graphite composites into Ni-Fe carbonate hydroxide (NiFe-CHs-CNT / G) via a green precipitation method, significantly improving the conductivity of the material. This composite material has an η... 10The overpotential is relatively low at 300mV. However, the preparation process of the above materials still requires cumbersome conditions such as high temperature and high pressure or heating and gas, which is not conducive to large-scale production. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing a high-efficiency and low-cost oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material that can be produced at room temperature and pressure. The second purpose of this invention is to provide the catalytic material. The third purpose of this invention is to provide the application of the catalytic material.

[0005] Technical solution: The preparation method of the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material of the present invention is as follows: nickel nitrate hexahydrate, potassium trioxalate ferrate and carbon nanotubes are dispersed in methanol solution, ultrasonically treated, and stirred at room temperature to obtain a mixed solution with precipitate. The obtained mixed solution is centrifuged, washed with methanol, and vacuum dried to obtain the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material.

[0006] This invention utilizes the coordination effect of oxalic acid groups to prepare oxalic acid-bridged Ni and Fe bimetallic coordination polymers in a one-step synthesis method. The raw materials are inexpensive and readily available, do not require pyrolysis heating, and can be prepared at room temperature and pressure. The preparation process is simple, economical, and safe.

[0007] Specifically, nickel nitrate hexahydrate, potassium trioxalatoferrate, and carbon nanotubes were dispersed in a methanol solution using a one-step method. This one-step preparation process is simple and efficient.

[0008] Specifically, the molar ratio of nickel, iron and carbon nanotubes is 2:1:1.2 to 480, and the mass percentage of carbon nanotubes in the prepared catalytic material is 2% to 90%.

[0009] More specifically, the molar ratio of nickel, iron and carbon nanotubes is 2:1:22.5 to 80, and the mass percentage of carbon nanotubes in the prepared catalytic material is 30% to 60%.

[0010] Specifically, the ultrasonic treatment time is 8 to 12 minutes, and the vacuum drying temperature is 50 to 70°C.

[0011] More specifically, the ultrasonic treatment time is 10 minutes, and the vacuum drying temperature is 60℃.

[0012] The catalytic material prepared by the above-mentioned method for preparing oxalate-based nickel-iron MOF doped carbon nanotube catalytic material has Ni and Fe bridged by oxalate ligands in the nickel-iron MOF.

[0013] Specifically, nickel-iron MOFs are doped with carbon nanotubes in the form of micro-nano particles with a particle size of 5 nm to 1 μm.

[0014] Specifically, the mass percentage of carbon nanotubes ranges from 2% to 90%.

[0015] Oxalic acid-based oxygen bridges participate in the synergistic effect between Ni and Fe bimetals. After incorporation of carbon nanotubes, the active sites of this catalyst material are fully exposed.

[0016] This invention also provides the application of the above-mentioned oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material in the alkaline water electrolysis oxygen evolution reaction (OER). The Ni / Fe bimetal linked by oxygen bridges can fully utilize the synergistic effect between the two. After combining with the active intermediate in the OER process, it can significantly reduce the thermodynamic energy barrier of its multi-electron transfer process, thereby accelerating the kinetic rate and exhibiting highly efficient OER catalytic performance.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0018] (1) By utilizing the coordination of oxalic acid groups, the structural environment between nickel and iron bimetals can be adjusted at the microscopic molecular level and the synergistic effect between them can be optimized. The structure-activity relationship of the catalyst material is easier to elucidate and analyze. Compared with existing catalyst materials with complex phase composition, it has greater advantages in structural regulation and better feasibility for catalytic mechanism research.

[0019] (2) Reducing the dependence of catalytic performance on specific nanostructures of materials can effectively resist adverse factors such as nanoparticle agglomeration and nanosheet stacking that cause performance degradation, thereby improving the stability and durability of catalyst materials.

[0020] (3) The raw materials are inexpensive and readily available, and can be prepared in one step without the need for pyrolysis heating. The preparation process is simple, economical, safe and reproducible, which is conducive to the large-scale production of the catalyst material.

[0021] (4) It has excellent OER catalytic performance in alkaline electrolyte. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope (SEM) image of the catalyst material prepared according to Example 4.

[0023] Figure 2 The image shows a transmission electron microscope (TEM) image of the Ni-Fe MOF / 30% CNT catalyst prepared according to Example 4.

[0024] Figure 3 The images show the X-ray diffraction (XRD) patterns of the catalytic materials prepared in Examples 1-5.

[0025] Figure 4 The OER polarization curves of the catalytic materials prepared in Examples 1-5 in 1.0M KOH solution are shown. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Example 1:

[0028] 1.2 mmol Ni(NO3)2·6H2O and 0.6 mmol K3[Fe(C2O4)3]·3H2O were dispersed in 25 mL of methanol solution. After sonication for 10 minutes, the mixture was stirred at room temperature for 12 hours to obtain a mixed solution with a green precipitate. The resulting mixed solution was centrifuged at 6000 rpm for 5 minutes and washed several times with methanol. Then, it was vacuum dried at 60 °C for 12 hours to obtain the catalyst precursor Ni-Fe MOF.

[0029] The X-ray diffraction pattern of the electrocatalytic material precursor prepared in this embodiment is as follows: Figure 3 As shown, the oxygen evolution performance was tested in an alkaline electrolyte solution (1.0 M KOH). In this embodiment, the oxygen evolution overpotential η in 1 M KOH was measured. 10 The voltage is approximately 300mV. The specific testing process is as follows:

[0030] Catalytic performance testing: The oxygen evolution performance (OER) of the catalyst material was tested under a standard three-electrode system, with a glassy carbon electrode (φ: 5mm) supporting the catalyst material as the working electrode, a graphite carbon rod as the counter electrode, and an HgO / Hg electrode as the reference electrode. The OER polarization curves are shown below. Figure 4 As shown.

[0031] Example 2:

[0032] 1.2 mmol Ni(NO3)2·6H2O, 0.6 mmol K3[Fe(C2O4)3]·3H2O and 0.72 mmol carbon nanotubes (CNTs) were dispersed in 25 mL of methanol solution. After sonication for 10 minutes, the mixture was stirred at room temperature for 12 hours to obtain a mixed solution with a gray-green precipitate. The resulting mixed solution was centrifuged at 6000 rpm for 5 minutes and washed several times with methanol. Then, it was vacuum dried at 60 °C for 12 hours to obtain the catalyst Ni-Fe MOF / 2%CNT.

[0033] The mass percentage of CNTs in the product was calculated to be 2% based on the experimental reaction.

[0034] The X-ray diffraction pattern of the electrocatalytic material prepared in this embodiment is as follows: Figure 3 As shown, the oxygen evolution performance was tested in an alkaline electrolyte solution (1.0 M KOH). In this embodiment, the oxygen evolution overpotential η in 1 M KOH was measured. 10 The voltage was 260mV. The specific testing process is as follows:

[0035] Catalytic performance testing: The oxygen evolution performance (OER) of the catalyst material was tested under a standard three-electrode system, with a glassy carbon electrode (φ: 5mm) supporting the catalyst material as the working electrode, a graphite carbon rod as the counter electrode, and an HgO / Hg electrode as the reference electrode. The OER polarization curves are shown below. Figure 4 As shown.

[0036] Example 3:

[0037] Unlike Example 2, the reaction raw materials were: 1.2 mmol Ni(NO3)2·6H2O, 0.6 mmol K3[Fe(C2O4)3]·3H2O and 3.6 mmol carbon nanotubes (CNTs); after stirring, a mixed solution with dark gray precipitate was obtained; finally, the catalyst material Ni-Fe MOF / 10% CNT was obtained.

[0038] The mass percentage of CNTs in the product was calculated to be 10% based on the experimental reaction.

[0039] The X-ray diffraction pattern of the electrocatalytic material prepared in this embodiment is as follows: Figure 3 As shown, the oxygen evolution performance was also tested in an alkaline electrolyte solution (1.0 M KOH). In this embodiment, the oxygen evolution overpotential η in 1 M KOH was measured. 10 The value is 250mV, and its OER polarization curve is also as shown. Figure 4 As shown.

[0040] Example 4:

[0041] Unlike Example 2, the reaction raw materials were: 0.32 mmol Ni(NO3)2·6H2O, 0.16 mmol K3[Fe(C2O4)3]·3H2O and 3.6 mmol carbon nanotubes (CNTs); the ultrasonic treatment time was 8 min; after stirring, a mixed solution with black precipitate was obtained; the vacuum drying temperature was 70 °C; and the final catalyst material Ni-Fe MOF / 30% CNT was obtained.

[0042] The mass percentage of CNTs in the product was calculated to be 30% based on the experimental reaction.

[0043] The X-ray diffraction pattern of the electrocatalytic material prepared in this embodiment is as follows: Figure 3 As shown, the oxygen evolution performance was tested in an alkaline electrolyte solution (1.0 M KOH), and its OER polarization curve is shown in the figure. Figure 4 As shown. Figure 1 This is a scanning electron microscope (SEM) image of the catalytic material prepared in Example 4. Figure 2 Transmission electron microscopy (TEM) image of the Ni-Fe MOF / 30% CNT catalyst material prepared for this embodiment. Figure 1 and Figure 2 As can be seen from the image, the catalytic material is Ni-Fe MOF doped with carbon nanotubes in the form of micro-nano particles with a particle size of 5nm to 1μm. This size can be directly measured from the transmission electron microscope (TEM) image and the scanning electron microscope (SEM) image.

[0044] The oxygen evolution overpotential of the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material prepared in this embodiment was tested in an alkaline electrolyte solution (1.0 M KOH).

[0045] The oxygen evolution overpotential η in 1 M KOH was measured. 10 With a value of only 240mV, it is superior to or close to most nickel-iron-based catalyst materials synthesized under more complex conditions.

[0046] Example 5:

[0047] Unlike Example 2, the reaction raw materials were: 0.09 mmol Ni(NO3)2·6H2O, 0.045 mmol K3[Fe(C2O4)3]·3H2O and 3.6 mmol carbon nanotubes (CNTs); after stirring, a mixed solution with black precipitate was obtained; finally, the catalyst material Ni-Fe MOF / 60% CNT was obtained.

[0048] The mass percentage of CNTs in the product was calculated to be 60% based on the experimental reaction.

[0049] The X-ray diffraction pattern of the electrocatalytic material prepared in this embodiment is as follows: Figure 3 As shown, the oxygen evolution performance was tested in an alkaline electrolyte solution (1.0 M KOH). In this embodiment, the oxygen evolution overpotential η in 1 M KOH was measured. 10 The value is 250mV, and its OER polarization curve is shown below. Figure 4 As shown.

[0050] Example 6:

[0051] Unlike Example 2, the reaction raw materials were: 0.015 mmol Ni(NO3)2·6H2O, 0.0075 mmol K3[Fe(C2O4)3]·3H2O and 3.6 mmol carbon nanotubes (CNTs); the ultrasonic treatment time was 12 min; after dispersing in 25 mL methanol solution and stirring for 12 hours, a black precipitate was obtained; the vacuum drying temperature was 50 °C; and the final catalyst material Ni-Fe MOF / 90% CNT was obtained.

[0052] The mass percentage of CNTs in the product was calculated to be 90% based on the experimental reaction.

[0053] The X-ray diffraction pattern of the electrocatalytic material prepared in this embodiment is as follows: Figure 3As shown, the oxygen evolution performance was tested in an alkaline electrolyte solution (1.0 M KOH). In this embodiment, the oxygen evolution overpotential η in 1 M KOH was measured. 10 The value is 270mV, and its OER polarization curve is shown in the figure. Figure 4 As shown.

[0054] Comparative Example 1:

[0055] Carbon nanotubes (CNTs) were used to test their oxygen evolution performance in an alkaline electrolyte solution (1.0 M KOH) under the same test conditions as in the above embodiments. In this embodiment, the oxygen evolution overpotential η in 1 M KOH was measured. 10 Above 500mV, there is no catalytic performance, and its OER polarization curve is also as shown. Figure 4 As shown.

[0056] Comparative Example 2:

[0057] The oxygen evolution performance (OER) of the commercial IrO2 catalyst in an alkaline electrolyte solution (1.0 M KOH) was tested under the same test conditions as in the examples above, and the OER polarization curves are as follows. Figure 4 As shown.

[0058] Oxygen evolution overpotential η of commercial IrO2 catalyst in 1MKOH 10 With an OER value of 330mV, it can be seen that the OER performance of Example 4 is significantly better than that of the commercial IrO2 catalyst.

[0059] In the above embodiments, the Ni-Fe MOF catalyst in Example 1 also has a low oxygen evolution overpotential in 1MKOH, but it is not doped with CNTs and has poor stability. In addition, the Ni-Fe MOF / 2%CNT catalyst in Example 2, the Ni-Fe MOF / 10%CNT catalyst in Example 3, and the Ni-Fe MOF / 90%CNT catalyst in Example 6 have very low oxygen evolution overpotentials in 1MKOH. Although they are slightly higher than the potential in Example 4, their performance is still better than that of the commercial IrO2 catalyst.

Claims

1. A method for preparing an oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material, characterized in that, Nickel nitrate hexahydrate, potassium trioxalate ferrate, and carbon nanotubes were dispersed in a methanol solution, sonicated, and stirred at room temperature to obtain a mixed solution with precipitate. The resulting mixed solution was centrifuged, washed with methanol, and vacuum dried to obtain oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material. The molar ratio of nickel, iron, and carbon nanotubes was 2:1:1.2~480.

2. The method for preparing the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material according to claim 1, characterized in that, Nickel nitrate hexahydrate, potassium trioxalate ferrate and carbon nanotubes were dispersed in a one-step process.

3. The method for preparing the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material according to claim 2, characterized in that, The mass percentage of carbon nanotubes in the prepared catalytic material is 2% to 90%.

4. The method for preparing the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material according to claim 3, characterized in that, The molar ratio of nickel, iron and carbon nanotubes is 2:1:22.5~80, and the mass percentage of carbon nanotubes in the prepared catalytic material is 30%~60%.

5. The method for preparing the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material according to claim 2, characterized in that, The ultrasonic treatment time is 8~12 minutes, and the vacuum drying temperature is 50~70℃.

6. The method for preparing the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material according to claim 1, characterized in that, In nickel-iron MOFs, Ni and Fe are bridged by oxalate ligands.

7. The method for preparing the oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material according to claim 1, characterized in that, Nickel-iron MOFs are doped with carbon nanotubes in the form of micro-nano particles with a particle size of 5 nm to 1 μm.

8. An oxalate-based nickel-iron MOF-doped carbon nanotube catalytic material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the catalytic material prepared by the method of claim 1, which is based on nickel iron oxalate MOF doped carbon nanotube catalytic material, in the alkaline water electrolysis oxygen evolution reaction.

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