CN117512676B - Hierarchical iron doped nickel-carbon structure nanotube and preparation method and application thereof - Google Patents

Abstract

The invention relates to a hierarchical iron-doped nickel-carbon structure nanotube, a preparation method and application thereof, wherein an in-situ grown iron-doped Ni-MOF@NF precursor is prepared from pretreated foam nickel through ion etching, and the surface of the calcined iron-doped Ni-MOF@NF precursor is converted into an Fe-Ni@C/NF hollow nanotube with excellent difunctional electrolyzed water catalytic capability. The invention synthesizes the Fe-doped Ni-MOF by utilizing the redox micro-reaction of the Fe ions on the surface of the foam nickel under the condition of not introducing exogenous Ni salt. The requirement of synthesizing the Ni-MOF of the nanotube morphology is met by adjusting the concentration of ferric salt. In addition, the doping of Fe is beneficial to improving the local electron distribution of active sites, improves the performance and efficiency of hydrogen and oxygen evolution, and has good performance as a catalyst of electrolyzed water.

Description

A graded iron-doped nickel-carbon structure nanotube and its preparation method and application

Technical field

The invention relates to the technical field of alkaline electrocatalytic water splitting, and in particular to a hierarchical iron-doped nickel-carbon structure nanotube and its preparation method and application.

Background technique

The increasing consumption of fossil fuels and its associated environmental issues such as air pollution, global warming, and rising sea levels have prompted the exploration and development of safe, clean, and renewable energy systems. Hydrogen can be used as a zero-carbon energy carrier. Hydrogen with high energy density is considered a promising energy choice. Among them, electrocatalytic water splitting to produce hydrogen is a promising green approach. The overall water splitting can be divided into two half-reactions, including the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Compared with HER, a larger thermodynamic potential is usually required to overcome the slow kinetics of OER due to its four-electron and four-proton transfer processes. The resulting high overpotential inevitably increases the cost and hinders the overall water splitting reaction. efficiency, thereby inhibiting the economical industrial production of hydrogen from electrolysis of water.

At present, noble metal catalysts such as ruthenium-based and platinum-based catalysts have been identified as efficient HER/OER catalysts, but their scarcity, high cost, and low stability severely limit their widespread application. Therefore, the development of noble metal-free materials as alternative HER/OER electrocatalysts is of great significance to achieve large-scale commercialization of water electrolysis.

As highly ordered coordination polymers, metal-organic frameworks (MOFs), as self-assemblies of metal ions and organic linkers, have the characteristics of both homogeneous and heterogeneous catalysts due to their high specific surface area and abundant pores. Their structures, diverse compositions and well-defined metal centers make them candidate materials for HER/OER catalysts. In particular, high specific surface area facilitates exposure of more active sites, porous structure allows rapid mass transport, and well-defined metal centers are essential for kinetic studies. These properties also endow MOFs with additional capabilities to serve as ideal templates/precursors for various carbon-related nanoelectrocatalysts via pyrolysis under atmosphere. MOF-derived hybrid materials tend to inherit the original morphology and develop into a porous structure, with active sites having a higher exposed area to the electrolyte, while the organic ligand-derived nanocarbonaceous matrix can enhance the electronic conductivity of the material.

A Chinese patent application discloses a preparation method for a self-supporting Ni-MOF-derived Ni ₃ C/Ni heterojunction electrocatalyst for water splitting (application number is 202310707523.9). The application uses precursor hydrothermal synthesis and subsequent nitrogen atmosphere Obtained by calcination, more energy is consumed in the synthesis step.

A Chinese patent application discloses a preparation method based on a nickel-based three-dimensional metal organic framework catalyst and the application of electrolysis of water for oxygen evolution based on this catalyst (application number is 201711472653. The nickel surface is coated with polyaniline, which is used as a template to undergo a multi-step reaction to form Ni@Co ₂ O ₃ /CN. The preparation steps are complicated.

In addition, the above-mentioned existing technologies all use other metal salts to synthesize metal organic frameworks to coat nickel foam ex-situ, and the combination with the nickel foam base is not tight enough.

Contents of the invention

In order to solve the above problems, the purpose of the present invention is to provide a hierarchical iron-doped nickel-carbon structure nanotube and its preparation method and application. The present invention uses nickel foam as the nickel source and substrate, and forms a self-contained nanotube through micro-reactions of ion exchange. The derived hollow nanotube arrays with controllable size are simultaneously incorporated with some iron elements to improve the local electron distribution. By adjusting the metal ion concentration, the iron doping content and the size of Ni-MOF hollow nanotubes can be adjusted simultaneously.

In order to achieve the above object, the present invention discloses a preparation method of hierarchical iron-doped nickel-carbon structure nanotubes, which includes the following steps:

(1) Pretreatment of nickel foam: immerse the nickel foam in an acid solution and wash it ultrasonically. After the ultrasound is completed, rinse it alternately with deionized water and absolute ethanol; then immerse the nickel foam in an organic solvent and wash it ultrasonically. After the ultrasound is completed, rinse it again. Use deionized water and absolute ethanol to alternately rinse, and put the rinsed nickel foam into a vacuum oven to dry to obtain pretreated nickel foam;

(2) Ion etching: Add diacetyl oxime and hydrated iron salt to absolute ethanol to prepare solution A; immerse the pretreated nickel foam obtained in step (1) into solution A and let stand at room temperature. Set the reaction, take it out after the reaction and put it into a vacuum oven to dry, to obtain the self-derived iron-doped Ni-MOF@NF precursor;

(3) Calculate the self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) in a nitrogen-hydrogen mixed atmosphere. After the calcination is completed, it is naturally cooled to room temperature, and the cooled material is washed. Put it into a vacuum oven and dry it to obtain hierarchical iron-doped nickel-carbon structure nanotubes, that is, a self-derived hollow nanotube array-coated nickel foam material, recorded as Fe-Ni@C/NF.

Further, in step (1), the foamed nickel is immersed in an acid solution and ultrasonic washed to remove impurities and oxides on the surface; the foamed nickel is immersed in an acetone solvent and ultrasonic washed to remove organic impurities on the surface; deionized water and non-ionized water are used. The number of alternating rinses with water and ethanol is three times;

Further, in step (1), the thickness of the nickel foam is 1 mm, the average pore diameter is 100 μm, the acid solution is hydrochloric acid solution, and the concentration of the acid solution is 2~6 mol/L; the organic solvent is acetone with a weight fraction of 98%; ultrasonic The washing time is 10~30 minutes, the drying temperature of the vacuum oven is 50~80℃, and the drying time is 4~12 hours.

Further, the hydrated iron salt for ion etching in step (2) includes at least one of nonahydrated ferric nitrate, hydrated ferric sulfate or heptahydrated ferrous sulfate, and the concentration of the iron salt in solution A is 0.001~0.013 mol. /L; the concentration of diacetyl oxime in solution A is 0.04~0.2 mol/L; the reaction time of the pretreated nickel foam immersed in solution A is 6~48 hours; the drying temperature of the vacuum oven is 50 ~80℃, drying time is 4~12 hours.

Further, the calcination temperature in step (3) is 200~500°C, the heating rate is 2~10°C/min, and the holding time is 1~4 hours.

Further, in step (3), the volume fraction of hydrogen in the nitrogen-hydrogen mixed atmosphere is 1%~20%, the working pressure of the nitrogen-hydrogen mixed atmosphere is 1~101 kPa, and the drying temperature of the vacuum oven is 40~80°C. Drying time is 12~24 hours.

The cleaning in step (3) is to remove the remaining uncoated powder impurities on the surface after calcination. Specifically, deionized water and absolute ethanol are used to alternately clean until the washing liquid is clear.

The invention also discloses a hierarchical iron-doped nickel-carbon structure nanotube prepared according to the above method and the hierarchical iron-doped nickel-carbon structure nanotube used as a catalyst to electrolyze water for hydrogen evolution reaction and oxygen evolution reaction in an alkaline environment. applications in.

The technical key points of the preparation method of hierarchical iron-doped nickel-carbon structure nanotubes of the present invention are:

(1) Control stable self-derived and size-controllable hollow nanotube-like materials on nickel foam;

(2) The relationship between the size of the hollow nanotubes and the calcination temperature is coordinated to maintain the overall tubular structure and no structural changes occur even after calcination, thereby forming Fe-Ni@C/NF with a hollow nanotube structure.

The invention discloses a method for preparing hierarchical iron-doped nickel-carbon structure nanotubes. The pretreated nickel foam is subjected to ion etching to first prepare an in-situ grown iron-doped Ni-MOF@NF precursor, and then the iron-doped Ni-MOF@NF precursor is prepared. The doped Ni-MOF@NF precursor is calcined at low temperature in a nitrogen-hydrogen mixed atmosphere, and then naturally cooled to room temperature. The cooled material is cleaned and dried, and finally Fe-Ni@C with a self-derived hollow nanotube structure is obtained. /NF material. This preparation method utilizes the characteristic binding properties of diacetyl oxime ligands to generate self-derived iron ion-doped Ni-MOF@NF precursors with hollow nanotubular structures through simple ion etching at room temperature, and then through One-step calcination process can produce a stable target product, and the material can still maintain a tubular structure after calcination, which increases the reaction area of the catalyst and retains as many active sites as possible. In Fe-Ni@C/NF, the role of nickel foam is to serve as a substrate for the uniform in-situ growth of the material and a nickel source to form iron-doped Ni-MOF, and to facilitate the rapid derivation of bubbles. Iron-doped active nickel nanoparticles play a synergistic catalytic role in the hydrogen evolution reaction and oxygen evolution reaction of electrolyzed water. Iron ions are an important element in the doping and etching steps. By adjusting the concentration of iron ions, the doping can be improved. The content and Ni-MOF morphology are controlled.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The steps of the preparation method of the present invention are simple and repeatable, the raw materials are cheap and easy to prepare, the products and by-products are harmless and easy to recover, and have wide application potential.

(2) Compared with commercially available precious metal catalysts commonly used in electrolysis water, the raw materials used in the method of preparing Fe-Ni@C/NF of the present invention all retain greater earth abundance, achieving better performance while saving production costs. , by regulating the activity and exposed area of the active sites, it can achieve approximately the same performance as precious metals.

(3) The contact area between commercially available bulk catalysts used in electrolysis water and the electrolyte is small. The Fe-Ni@C/NF material prepared by the present invention has a hollow nanotube structure, and the doping ratio and proportion are controlled by adjusting the concentration of iron ions. Ni-MOF size, thereby optimizing the synthesis of a total water splitting catalyst with the best specific surface area and local site activity.

(4) Compared with pure nickel foam and iron-doped Ni-MOF@NF precursor, Fe-Ni@C/NF has better hydrophilicity and lower impedance, so it has better conductivity , which can accordingly improve the efficiency of hydrogen and oxygen evolution in electrolytic water in an alkaline environment.

(5) Compared with powder materials, the Fe-Ni@C/NF finally obtained by the present invention is a self-derived nickel foam support material. This material can not only promote the discharge of bubbles on the surface catalyst, but also can be used directly as a working electrode to avoid It eliminates material debugging, coating, drying and other operations, saves catalyst preparation time, avoids some losses caused by coating electrodes, and further reduces costs.

(6) Compared with single metal or pure phase catalyst materials, the addition of Fe in Fe-Ni@C/NF optimizes the local electron distribution of the active site. The presence of multivalent ions in this catalyst material is conducive to reducing hydrogen, Potential barrier in the oxygen binding process.

(7) The Fe-Ni@C/NF prepared by the present invention has relatively excellent electrocatalytic water splitting properties for hydrogen evolution and oxygen evolution, and can maintain good stability. The HER performance is close to commercial carbon-supported platinum at the same load. The OER performance is close to that of commercial ruthenium oxide at the same loading.

(8) Different from other methods of synthesizing metal-organic frameworks with metal salts to ex-situ coat nickel foam, the nanostructure formed by self-derivatization of in-situ metal-organic frameworks using ion etching to coat nickel foam is more uniform and is consistent with the nickel foam substrate. The binding is tighter, the doping amount and Ni-MOF precursor size are controllable by adjusting the iron ion concentration, and no additional nickel salt is required. The preparation method of the present invention is universal and can be used with widely used transition metal salts to form iron-doped Ni-MOF@NF by a self-derivatization method.

Description of the drawings

Figure 1 is an SEM image of the self-derived iron-doped Ni-MOF@NF precursor prepared in Example 3 and Comparative Examples 1 and 2 respectively. The numbers 1 and 2 in the upper left corner are those prepared in Example 3, and the number 3 in the upper left corner is , 4 are prepared in Comparative Example 2, and numbers 5 and 6 in the upper left corner are prepared in Comparative Example 1;

Figure 2 is an SEM image of the self-derived iron-doped Ni-MOF@NF precursor prepared in Examples 1 to 3. The upper left corner marked with 0.001M FeSO ₄ corresponds to Example 1, and the upper left corner marked with 0.005M FeSO ₄ corresponds to In Example 2, the mark on the upper left corner with 0.01M FeSO ₄ corresponds to Example 3;

Figure 3 is an SEM image of the Fe-Ni@C/NF material prepared in Example 3;

Figure 4 is the Raman spectrum of the Fe-Ni@C/NF material prepared in Example 3;

Figure 5 is an XPS pattern of the self-derived iron-doped Ni-MOF@NF precursor prepared in Example 3, in which the number 1 in the upper left corner is the full spectrum, and the number 2 in the upper left corner is the Ni 2p orbital XPS fine spectrum. Corner number 3 is the Fe 2p orbital XPS fine spectrum;

Figure 6 is the XRD pattern of the self-derived iron-doped Ni-MOF@NF precursor and Fe-Ni@C/NF material prepared in Example 3;

Figure 7 shows the Fe-Ni@C/NF material prepared in Example 3, the Fe-Ni@C/NF-S obtained in Comparative Example 1, and the Fe-Ni@C/NF-N, Pt/ LSV curve of hydrogen evolution reaction of C/NF in alkaline environment;

Figure 8 is the LSV curve of the oxygen evolution reaction of RuO ₂ /NF and the Fe-Ni@C/NF material prepared in Example 3 in an alkaline environment;

Figure 9 is the it stability test curve of the Fe-Ni@C/NF material prepared in Example 3 during the oxygen evolution reaction in an alkaline environment at a current density of 60 mA cm ^-2 .

Detailed ways

In order to better understand the content of the present invention, the present invention will be further explained below in conjunction with specific embodiments and drawings. The following examples are implemented based on the technology of the present invention and provide detailed implementation modes and operating steps. However, the protection scope of the present invention is not limited to the following examples.

Example 1:

(1) Pretreatment of nickel foam: Immerse the nickel foam of 10mm×10mm×1mm with a pore diameter of about 100μm into 15mL of hydrochloric acid solution with a substance concentration of 3 mol/L and wash it ultrasonically for 20 minutes, then use deionized water and anhydrous Alternately rinse with ethanol three times; then immerse the foamed nickel in 15 mL of acetone solvent with a weight fraction of 98% and ultrasonically wash for 20 minutes, then rinse alternately with deionized water and absolute ethanol three times; put the rinsed foamed nickel into a vacuum oven. Dry at 60°C for 12 hours to obtain pretreated nickel foam;

(2) Ion etching: Dissolve 0.1742g diacetyl oxime and 0.0028g ferrous sulfate heptahydrate in 10 mL absolute ethanol to prepare solution A; immerse the pretreated nickel foam obtained in step (1) into the solution A and left to react at room temperature for 6 hours, then take out the reacted nickel foam in solution A and place it in a vacuum oven to dry at 60°C for 12 hours to obtain the self-derivatized iron-doped Ni-MOF@NF precursor. ;

(3) Calculate the self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) in a nitrogen-hydrogen mixed atmosphere with a hydrogen volume fraction of 2% and a standard atmospheric pressure, with a heating rate of 5°C/ min, the calcination temperature is 300°C, and the holding time is 1 hour. After the calcination is completed, it is naturally cooled to room temperature. The cooled material is washed three times alternately with deionized water and absolute ethanol. The washing liquid is clarified, and then placed in a vacuum oven. After drying at 60°C for 6 hours, a hierarchical iron-doped nickel-carbon structure nanotube was obtained, which is a self-derived hollow nanotube-coated nickel foam material, recorded as Fe-Ni@C/NF.

Example 2:

(1) Pretreatment of nickel foam: Immerse the nickel foam of 10mm×10mm×1mm with a pore diameter of about 100μm into 15mL of hydrochloric acid solution with a substance concentration of 3 mol/L and wash it ultrasonically for 20 minutes, then use deionized water and anhydrous Alternately rinse with ethanol three times; then immerse the foamed nickel in 15 mL of acetone solvent with a weight fraction of 98% and ultrasonically wash for 20 minutes, then rinse alternately with deionized water and absolute ethanol three times; put the rinsed foamed nickel into a vacuum oven. Dry at 60°C for 12 hours to obtain pretreated nickel foam;

(2) Ion etching: Dissolve 0.1742g diacetyl oxime and 0.0139g ferrous sulfate heptahydrate in 10mL absolute ethanol to prepare solution A; immerse the pretreated nickel foam obtained in step (1) into the solution A and left to react at room temperature for 12 hours, then take out the reacted nickel foam in solution A and place it in a vacuum oven to dry at 60°C for 12 hours to obtain the self-derivatized iron-doped Ni-MOF@NF precursor. ;

(3) Calculate the self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) in a nitrogen-hydrogen mixed atmosphere with a hydrogen volume fraction of 15% and a standard atmospheric pressure, with a heating rate of 5°C/ min, the calcination temperature is 250°C, and the holding time is 1 hour. After the calcination is completed, it is naturally cooled to room temperature. The cooled material is washed three times with deionized water and absolute ethanol alternately. The washing liquid is clarified, and then placed in a vacuum oven. After drying at 60°C for 6 hours, a hierarchical iron-doped nickel-carbon structure nanotube was obtained, which is a self-derived hollow nanotube-coated nickel foam material, recorded as Fe-Ni@C/NF.

Example 3:

(1) Pretreatment of nickel foam: Immerse the nickel foam of 10mm×10mm×1mm with a pore diameter of about 100μm into 15mL of hydrochloric acid solution with a substance concentration of 3 mol/L and wash it ultrasonically for 20 minutes, then use deionized water and anhydrous Alternately rinse with ethanol three times; then immerse the foamed nickel in 15 mL of acetone solvent with a weight fraction of 98% and ultrasonically wash for 20 minutes, then rinse alternately with deionized water and absolute ethanol three times; put the rinsed foamed nickel into a vacuum oven. Dry at 60°C for 12 hours to obtain pretreated nickel foam;

(2) Ion etching: Dissolve 0.1742g diacetyl oxime and 0.0278g ferrous sulfate heptahydrate in 10 mL absolute ethanol to prepare solution A; immerse the pretreated nickel foam obtained in step (1) into the solution A and left to react at room temperature for 24 hours, then take out the reacted nickel foam in solution A and place it in a vacuum oven to dry at 60°C for 12 hours to obtain the self-derivatized iron-doped Ni-MOF@NF precursor. ;

(3) The self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) is calcined in a nitrogen-hydrogen mixed atmosphere with a hydrogen volume fraction of 5% and a standard atmospheric pressure, with a heating rate of 5°C/ min, the calcination temperature is 450°C, and the holding time is 1 hour. After the calcination is completed, it is naturally cooled to room temperature. The cooled material is washed three times with deionized water and absolute ethanol alternately. The washing liquid is clarified, and then placed in a vacuum oven. After drying at 60°C for 6 hours, a hierarchical iron-doped nickel-carbon structure nanotube was obtained, which is a self-derived hollow nanotube-coated nickel foam material, recorded as Fe-Ni@C/NF.

Example 4:

(1) Pretreatment of nickel foam: Immerse the nickel foam of 10mm×10mm×1mm with a pore diameter of about 100μm into 15mL of hydrochloric acid solution with a substance concentration of 3 mol/L and wash it ultrasonically for 20 minutes, then use deionized water and anhydrous Alternately rinse with ethanol three times; then immerse the foamed nickel in 15 mL of acetone solvent with a weight fraction of 98% and ultrasonically wash for 20 minutes, then rinse alternately with deionized water and absolute ethanol three times; put the rinsed foamed nickel into a vacuum oven. Dry at 60°C for 12 hours to obtain pretreated nickel foam;

(2) Ion etching: Dissolve 0.1742g diacetyl oxime, 0.0139g ferrous sulfate heptahydrate and ferric nitrate nonahydrate in 10mL absolute ethanol to prepare solution A; The treated nickel foam was immersed in solution A and left to react at room temperature for 48 hours. Then the reacted nickel foam in solution A was taken out and placed in a vacuum oven to dry at 60°C for 12 hours to obtain self-derived iron doping. Ni-MOF@NF precursor;

(3) The self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) is calcined in a nitrogen-hydrogen mixed atmosphere with a hydrogen volume fraction of 5% and a standard atmospheric pressure, with a heating rate of 5°C/ min, the calcination temperature is 450°C, and the holding time is 1 hour. After the calcination is completed, it is naturally cooled to room temperature. The cooled material is washed three times with deionized water and absolute ethanol alternately. The washing liquid is clarified, and then placed in a vacuum oven. After drying at 60°C for 6 hours, a hierarchical iron-doped nickel-carbon structure nanotube was obtained, which is a self-derived hollow nanotube-coated nickel foam material, recorded as Fe-Ni@C/NF.

Comparative example 1:

(1) Pretreatment of nickel foam: Immerse nickel foam with a size of 10mm×10mm×1mm and a pore diameter of about 100μm into 15mL of hydrochloric acid solution with a substance concentration of 3 mol/L and ultrasonic washing for 20 minutes, and then wash it with deionized water and sterile water. Rinse alternately with water and ethanol three times; then immerse the foamed nickel in 15 mL of acetone solvent with a weight fraction of 98% and wash ultrasonically for 20 minutes, then rinse alternately three times with deionized water and absolute ethanol; put the rinsed foamed nickel into a vacuum oven Dry at 60°C for 12 hours to obtain pretreated nickel foam;

(2) Ion etching: Dissolve 0.1742g diacetyl oxime and 0.0403g ferrous sulfate heptahydrate in 10mL absolute ethanol to prepare solution A; immerse the pretreated nickel foam obtained in step (1) into the solution A and left to react at room temperature for 12 hours, then take out the reacted nickel foam in solution A and place it in a vacuum oven to dry at 60°C for 12 hours to obtain the self-derivatized iron-doped Ni-MOF@NF precursor. ;

(3) The self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) is calcined in a nitrogen-hydrogen mixed atmosphere with a hydrogen volume fraction of 5% and a standard atmospheric pressure, with a heating rate of 5°C/ min, the calcination temperature is 300°C, and the holding time is 1 hour. After the calcination is completed, it is naturally cooled to room temperature. The cooled material is washed three times with deionized water and absolute ethanol alternately. The washing liquid is clarified, and then the material is placed in a vacuum Dry in an oven at 60°C for 6 hours, and the material obtained is designated as Fe-Ni@C/NF-S.

Comparative example 2:

(1) Pretreatment of nickel foam: Immerse the nickel foam of 10mm×10mm×1mm with a pore diameter of about 100μm into 15mL of hydrochloric acid solution with a substance concentration of 3 mol/L and wash it ultrasonically for 20 minutes, then use deionized water and anhydrous Alternately rinse with ethanol three times; then immerse the foamed nickel in 15 mL of acetone solvent with a weight fraction of 98% and ultrasonically wash for 20 minutes, then rinse alternately with deionized water and absolute ethanol three times; put the rinsed foamed nickel into a vacuum oven. Dry at 60°C for 12 hours to obtain pretreated nickel foam;

(2) Ion etching: Dissolve 0.1742g diacetyl oxime and 0.0404g iron nitrate nonahydrate in 10 mL absolute ethanol to prepare solution A; immerse the pretreated nickel foam obtained in step (1) into solution A neutralize and let stand for 12 hours at room temperature, then take out the reacted nickel foam in solution A and dry it in a vacuum oven at 60°C for 12 hours to obtain the self-derivatized iron-doped Ni-MOF@NF precursor.

(3) The self-derived iron-doped Ni-MOF@NF precursor obtained in step (2) is calcined in a nitrogen-hydrogen mixed atmosphere with a hydrogen volume fraction of 5% and a standard atmospheric pressure, with a heating rate of 5°C/ min, the calcination temperature is 300°C, and the holding time is 1 hour. After the calcination is completed, it is naturally cooled to room temperature. The cooled material is washed three times alternately with deionized water and absolute ethanol. The washing liquid is clarified, and then placed in a vacuum oven. Dry at 60°C for 6 hours, and the obtained material is designated as Fe-Ni@C/NF-N.

SEM testing was performed using a ZEISS GeminiSEM 300 scanning electron microscope from Zeiss, Germany. The self-derived iron-doped Ni-MOF@NF precursor was adhered to the sample stage coated with black conductive glue, and then sprayed with gold. SEM testing can analyze the microstructure of materials. Figure 1 is an SEM image of the self-derived iron-doped Ni-MOF@NF precursor prepared in Example 3 and Comparative Examples 1 and 2 respectively. The numbers 1 and 2 in the upper left corner are those prepared in Example 3, and the number 3 in the upper left corner is , 4 are prepared in Comparative Example 2, and those marked 5 and 6 in the upper left corner are prepared in Comparative Example 1. It can be seen from the figure that the pretreated NF can form MOFs with different morphologies in situ through different etching conditions. structure, in which 0.01M ferrous sulfate etching in Example 3 can form a size-controllable tube structure Ni-MOF@NF precursor, that is, a hollow nanotube array, and the Fe-Ni@C/NF- prepared in Comparative Example 2 N is a nanocone array, and the Fe-Ni@C/NF-S prepared in Comparative Example 1 is a nanocluster array.

Figure 2 is an SEM image of the self-derived iron-doped Ni-MOF@NF precursor prepared in Examples 1 to 3. The image shows that the integrity of the nanotube array formation can be affected by regulating the concentration of ferrous ions.

Figure 3 is an SEM image of the Fe-Ni@C/NF material prepared in Example 3. This image shows that after low-temperature calcination of the self-derived iron-doped Ni-MOF@NF precursor, the material can still maintain the tube structure, which is beneficial to Exposure of more catalytically active sites improves catalytic efficiency.

Figure 4 is a Raman spectrum of the Fe-Ni@C/NF material prepared in Example 3. In this figure, the calcined nanotubes on the surface are composed of a carbon skeleton coating the active ingredient.

The Scientific K-Alpha X-ray photoelectron spectrometer of the American Thermo Company was used for XPS testing. The self-derived iron-doped Ni-MOF@NF precursor was adhered to the sample stage to analyze the valence state and possibility of the surface elements of the material. bonding effect. The full spectrum labeled 1 in the upper left corner of Figure 5 shows that the self-derived iron-doped Ni-MOF@NF precursor can not only form Ni-MOF through ion etching, but also a small amount of iron doping will occur. The number 1 in the upper left corner of Figure 5 In the Ni 2p orbital XPS fine spectrum of 2, the Ni2p fine spectrum corresponds to the Ni-MOF characteristic peak, proving that Ni-MOF appears on the surface of the material. In the Fe 2p orbital XPS fine spectrum labeled 3 in the upper left corner of Figure 5, the Fe2p fine spectrum Corresponding to the successful doping of Fe element in Ni-MOF.

The Rigaku Ultima IV type X-ray diffractometer of Japan Rigaku Corporation was used for XRD testing. The self-derived material on the nickel foam was scraped off and evenly filled into the sample stage to analyze the composition of the material and the structure or morphology of the atoms or molecules inside the material. information. Figure 6 is the XRD pattern of the self-derived iron-doped Ni-MOF@NF precursor and Fe-Ni@C/NF material prepared in Example 1. The corresponding curves of the self-derived iron-doped Ni-MOF@NF precursor show that The iron-doped Ni-MOF@NF precursor has typical XRD characteristic peaks of DNi, indicating the successful synthesis of Ni-MOF after etching; Fe-Ni@C/NF corresponds to the XRD characteristic peaks, and there is an obvious corresponding to Ni(111) The 44.5° of the crystal plane corresponds to the 51.9° of the (200) crystal plane and the 76.4° of the (220) crystal plane. The incorporated Fe was not detected because the content was too low.

The pretreated nickel foam is obtained by using the method of step (1) in Example 3, and a certain mass of commercial 5%Pt/C is taken. The commercial 5%Pt/C is the same as the Fe-Ni@C/ obtained in Example 3. The mass of the surface active components of NF is equal (mass of the surface active components of Fe-Ni@C/NF obtained in Example 3 = mass of Fe-Ni@C/NF - mass of nickel foam after pretreatment in step (1) ), add the commercial 5% Pt/C to a mixed solution containing 480 μL absolute ethanol, 480 μL deionized water and 40 μL Nifion to form a suspension, and then apply the suspension dropwise on the pretreated nickel foam surface And it is dried by a solar lamp to obtain 5%Pt/C loaded with nickel foam, which is recorded as Pt/C/NF. The commercial 5%Pt/C belongs to the existing technology and will not be described again here.

Chenhua CHI760E was used to conduct electrochemical LSV testing on the materials. The Fe-Ni@C/NF material prepared in Example 3, the Fe-Ni@C/NF-S obtained in Comparative Example 1, and the Fe-Ni@C/NF material obtained in Comparative Example 2 were used. Ni@C/NF-N and the Pt/C/NF obtained above were analyzed for electrocatalytic hydrogen evolution and oxygen evolution capabilities. The specific implementation method is: use a traditional three-electrode system to test the material, in which the working electrode is a square electrode sheet cut and shaped into 10*10mm; a Φ6mm carbon rod is used as the counter electrode; and a Hg/HgO electrode is used as the reference electrode. Figure 7 shows that in 1 mol/L KOH solution, the nanotube array Fe-Ni@C/NF synthesized in Example 3 can reach a low overpotential of 30.2 mV-10 mA cm ^-2 after 80% IR compensation. It is better than the Fe-Ni@C/NF-S obtained in Comparative Example 1 and the Fe-Ni@C/NF-N obtained in Comparative Example 2. It is also better than the commercial 5% Pt/C precious metal supported by nickel foam.

The pretreated nickel foam is obtained using the method of step (1) in Example 3, and a certain mass of ruthenium oxide is obtained. The mass of the ruthenium oxide is equal to the surface active component of Fe-Ni@C/NF obtained in Example 3. (The mass of the surface active component of Fe-Ni@C/NF obtained in Example 3 = the mass of Fe-Ni@C/NF - the mass of the nickel foam after pretreatment in step (1)), add the ruthenium oxide A suspension was formed in a mixed solution containing 480 μL of absolute ethanol, 480 μL of deionized water and 40 μL of Nifion, and then the suspension was dropwise applied on the surface of the pretreated nickel foam and dried by sunlight to obtain the nickel foam loaded RuO ₂ , recorded as RuO ₂ /NF.

The LSV curve of the oxygen evolution reaction in Figure 8 shows that in 1 mol/L KOH solution, the Fe-Ni@C/NF obtained in Example 3 can reach 392 mV-200 mA cm ^-2 after 80% IR compensation. , indicating that Fe-Ni@C/NF has good oxygen evolution reaction kinetics, which is comparable to commercial RuO ₂ precious metal.

The it stability test curve in the oxygen evolution reaction in Figure 9 shows that at an oxidation current of 60 mA cm ^-2 , the Fe-Ni@C/NF prepared in Example 3 can react stably for more than 50 hours without performance degradation. This fully demonstrates the reaction stability of the material.

The above are only embodiments of the present invention, and do not limit the present invention in any form. The present invention can also have other forms of embodiments based on the above structures and functions, which will not be listed one by one. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention by any skilled person familiar with this field without departing from the scope of the technical solution of the present invention will still fall within the scope of the technical solution of the present invention. Inside.

Claims (6)

1. A preparation method of a hierarchical iron doped nickel-carbon structure nanotube is characterized by comprising the following steps of: the method specifically comprises the following steps:

(1) Pretreatment of foam nickel: immersing foam nickel into an acid solution for ultrasonic washing, and after the ultrasonic treatment is finished, alternately flushing by using deionized water and absolute ethyl alcohol; immersing the foam nickel into an organic solvent for ultrasonic washing, alternately flushing with deionized water and absolute ethyl alcohol after the ultrasonic treatment is finished, and putting the flushed foam nickel into a vacuum oven for drying to obtain pretreated foam nickel;

(2) Ion etching: respectively adding dimethylglyoxime and ferric salt hydrate into absolute ethyl alcohol to prepare a solution A; immersing the pretreated foam nickel obtained in the step (1) into the solution A, standing at room temperature for reaction, taking out the foam nickel after the reaction is finished, and putting the foam nickel into a vacuum oven for drying to obtain a self-derived iron doped Ni-MOF@NF precursor;

(3) Calcining the self-derived iron doped Ni-MOF@NF precursor in a nitrogen-hydrogen mixed atmosphere, naturally cooling to room temperature after calcining, cleaning the cooled substance, and then putting the substance into a vacuum oven for drying to obtain the graded iron doped nickel-carbon structure nanotube;

the ion etched ferric hydrate salt in the step (2) comprises at least one of ferric nitrate nonahydrate, ferric sulfate hydrate or ferrous sulfate heptahydrate, and the mass concentration of the ferric hydrate salt in the solution A is 0.001-0.013 mol/L; the mass concentration of the dimethylglyoxime in the solution A is 0.04-0.2 mol/L; the reaction time of immersing the pretreated foam nickel into the solution A is 0.1-24 hours; the drying temperature of the vacuum oven is 50-80 ℃ and the drying time is 4-12 hours;

the calcination temperature in the step (3) is 200-500 ℃, the heating rate is 2-10 ℃/min, and the heat preservation time is 1-4 hours.

2. The method for preparing the graded iron-doped nickel-carbon structure nanotube according to claim 1, wherein the method comprises the following steps: the thickness of the foam nickel in the step (1) is 1mm, the average pore diameter is 100 mu m, the acid solution is hydrochloric acid solution, and the concentration of the acid solution is 2-6 mol/L; the organic solvent is acetone with the mass fraction of 98%; the ultrasonic washing time is 10-30 minutes, the drying temperature of the vacuum oven is 50-80 ℃, and the drying time is 4-12 hours.

3. The method for preparing the graded iron-doped nickel-carbon structure nanotube according to claim 1, wherein the method comprises the following steps: in the step (3), the volume fraction of hydrogen in the nitrogen-hydrogen mixed atmosphere is 1% -20%, the working pressure of the nitrogen-hydrogen mixed atmosphere is 1% -101 kPa, the drying temperature of the vacuum oven is 40% -80 ℃, and the drying time is 12-24 hours.

4. The method for preparing the graded iron-doped nickel-carbon structure nanotube according to claim 1, wherein the method comprises the following steps: the washing in the step (3) is specifically carried out by adopting deionized water and absolute ethyl alcohol to alternately wash until the washing liquid is clear.

5. The graded iron-doped nickel-carbon nanotube prepared by the preparation method according to any one of claims 1 to 4.

6. The use of the graded iron-doped nickel-carbon structure nanotube according to claim 5 in an electrolytic water hydrogen evolution reaction and an oxygen evolution reaction in an alkaline environment.