CN117342532A - A tungsten-doped nickel phosphide nanosheet array material and its preparation and application - Google Patents

Abstract

The invention relates to a tungsten-doped nickel phosphide nanosheet array material and preparation and application thereof, wherein the preparation method comprises the following steps: (1) Dispersing metal precursor nickel salt, urea, ammonium fluoride and ammonium metatungstate solution in deionized water to form a uniform solution, transferring the uniform solution into a reaction kettle containing foam nickel, and carrying out hydrothermal reaction to obtain a tungsten-doped nickel single metal precursor loaded on the foam nickel; (2) And (3) placing the tungsten-doped nickel single-metal precursor loaded on the foam nickel in an argon atmosphere with sodium hypophosphite at high temperature for phosphating to obtain a tungsten-doped nickel phosphide nanosheet array material, namely the target product. The catalyst preparation method has low cost and easy operation, has good oxidation reaction (BAOR) and Hydrogen Evolution (HER) electrocatalysis performance of the benzylamine in alkaline electrolyte, and can selectively oxidize the benzylamine into the value-added benzonitrile with higher efficiency.

Description

A tungsten-doped nickel phosphide nanosheet array material and its preparation and application

Technical field

The invention belongs to the technical field of catalysts and relates to a tungsten-doped nickel phosphide nanosheet array material and its preparation and application.

Background technique

In recent years, the massive consumption of fossil energy in industrial production and daily life has led to serious environmental problems, including the greenhouse effect, air pollution, soil pollution, and water pollution. In order to solve these pressing problems, it is imperative to develop clean energy. Hydrogen (H ₂ ) is a promising solution due to its high calorific value and minimal environmental impact. Currently, there are several methods for hydrogen production, among which electrocatalytic water splitting is a particularly feasible method. The process includes two important half-reactions: oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Although non-noble metal OER electrocatalysts have been significantly developed, the four-electron OER process is slow and requires a higher potential, resulting in reduced energy conversion efficiency. In order to improve the yield of electrocatalytic hydrogen production, an effective strategy is to introduce easily oxidizable small molecules such as urea, hydrazine and alcohol near the anode. However, many of these products are hydrophilic, often occupying active sites, and are difficult to isolate. Furthermore, some of these molecules have relatively limited economic value.

Benzonitrile (BN) is of great significance as an intermediate in the production of fine chemicals, agrochemicals and pharmaceuticals, and has received widespread attention from academia and commercial sectors. Traditionally, the chemical synthesis of BN involves nucleophilic substitution reactions between organic matter and cyanide; however, the use of highly toxic reagents like cyanide has greatly limited its practical application. Recent studies have shown that the electrochemical oxidation of benzylamine (BA) provides a clean, efficient and selective route to produce BN. The obtained product BN is hydrophobic and can naturally float on the water surface, preventing fouling on the catalyst surface and facilitating large-scale synthesis. In addition, compared with OER, benzylamine oxidation reaction (BAOR) has obvious thermodynamic advantages and improves the hydrogen generation efficiency of the cathode.

Element doping is considered an effective method to design efficient electrocatalysts. Previous studies have proven that the doping of electron-deficient elements can promote electron transfer and optimize the adsorption/desorption energy of reagents or intermediates, thereby improving catalytic activity. In addition, high selectivity for small molecule oxidation can be improved. Therefore, it is possible to construct self-supporting catalysts by doping elements to create bifunctional electrocatalysts for hydrogen production and organic upgrading.

Therefore, it is very feasible to rationally design non-noble metal bifunctional catalysts for the simultaneous and efficient production of hydrogen and BN, and doping W atoms to improve the catalytic activity and high selectivity of the catalysts. Furthermore, this work not only provides a feasible strategy for exploring low-cost, abundant, and efficient electrocatalysts, but also provides innovative insights into the electrochemical synthesis of high-value nitrile compounds as well as hydrogen production.

The present invention is also proposed based on the above discussion.

Contents of the invention

The purpose of the present invention is to provide a tungsten-doped nickel phosphide nanosheet array material and its preparation and application. Thanks to the in-situ growth strategy and the array structure of the nanosheets, it is conducive to rapid electron transfer and exposes More active sites, and tungsten doping can attract electrons on nickel to accelerate the formation of trivalent nickel, which is beneficial to the catalytic activity of the material.

The object of the present invention can be achieved through the following technical solutions:

One of the technical solutions of the present invention provides a method for preparing a tungsten-doped nickel phosphide nanosheet array material, which includes the following steps:

(1) Disperse the metal precursor nickel salt and urea, ammonium fluoride, and ammonium metatungstate solutions in deionized water to form a uniform solution, and then transfer it to a reaction kettle containing nickel foam for hydrothermal reaction to obtain nickel foam loaded Tungsten-doped nickel monometallic precursor;

(2) The tungsten-doped nickel single metal precursor supported on the nickel foam is placed in an argon atmosphere with sodium hypophosphite upstream for high-temperature phosphating to obtain a tungsten-doped nickel phosphide nanosheet array material, which is target product.

Further, in step (1), the metal precursor nickel salt is nickel nitrate hexahydrate.

Further, in step (1), the ratio of the addition amounts of the metal precursors nickel salt, urea, ammonium fluoride, and ammonium metatungstate is (1-3) mmol: (5-7) mmol: (8-12) mmol: (10-20) mg.

Further, in step (1), the hydrothermal reaction temperature is 110-130°C and the time is 5-7 hours. Preferably, the hydrothermal reaction temperature is 120°C and the time is 6 hours.

Further, in step (1), the nickel foam is cleaned before being put into the reaction kettle.

Further, in step (2), the high-temperature phosphating temperature is 320-380°C and the phosphating time is 1-3h. Preferably, the phosphating temperature is 350°C and the phosphating time is 2h.

Furthermore, in step (2), the temperature rise rate during the high-temperature phosphating process is 5°C/min.

In the process of the present invention, nickel nitrate hexahydrate and ammonium metatungstate are used as metal sources, urea and ammonium fluoride are added reagents, and deionized water is used as the solvent. A piece of clean nickel foam is added to the reaction kettle. After the hydrothermal reaction is completed, , in-situ growth of tungsten-doped nickel single-metal nanosheet array structures on the surface of nickel foam. In addition, by adjusting the amount of ammonium metatungstate, nanosheet arrays of nickel hydroxide with different tungsten doping amounts can be obtained.

Finally, the above precursor is converted into a tungsten-doped nickel phosphide nanosheet array through high-temperature phosphating treatment. Too much tungsten doping will destroy the morphology of the nanosheets, leading to a reduction in active sites and reduced catalytic activity; too low a tungsten doping amount will result in a lower role of tungsten in the catalytic process.

The second technical solution of the present invention provides a tungsten-doped nickel phosphide nanosheet array material, which is prepared by any of the above preparation methods.

The third technical solution of the present invention provides the application of tungsten-doped nickel phosphide nanosheet array materials. The nanosheet array materials are used as bifunctional electrocatalysts in HER and BAOR under alkaline conditions.

Furthermore, the nanosheet array material is used to selectively oxidize benzylamine to generate value-added benzonitrile.

The in-situ growth strategy in the present invention avoids the use of adhesives, ensures close contact between the catalyst and the conductive substrate interface, and promotes rapid charge transfer. The regularly arranged nanosheet array structure is conducive to accelerating the diffusion and mass transfer of the catalytic reaction, accelerating the rapid desorption of accumulated bubbles, and having a large specific surface area, thereby fully exposing the active sites and improving reaction kinetics. The method involved is low cost, easy to operate, and the product has good electrocatalytic activity for hydrogen evolution (HER) and benzylamine oxidation (BAOR) in alkaline electrolyte, and can be used at the cathode and anode simultaneously at a lower voltage input. Enable the production of value-added chemicals.

Compared with the prior art, the present invention has the following advantages:

(1) The in-situ grown nanoarray structure has fast charge transfer and a large specific surface area, thereby effectively improving the electrocatalytic hydrogen evolution and benzylamine oxidation performance.

(2) The electron-rich nature of tungsten can attract electrons on nickel, promote charge transfer, and accelerate the formation of Ni ³⁺ , thereby effectively improving catalytic activity.

(3) Defect sites are created by reduction under an argon atmosphere, which is beneficial to capturing active substances, thereby improving the performance of electrocatalytic hydrogen evolution and benzylamine oxidation.

(4) W-Ni ₂ P can be used as a bifunctional catalyst. It not only has excellent HER catalytic activity, but also can effectively electrocatalyze the oxidation reaction of benzylamine, achieving effective catalytic oxidation of benzylamine at the anode under lower voltage input. , while efficiently producing hydrogen at the cathode, high value-added benzonitrile is produced at the anode.

Description of drawings

Figure 1-1 is a scanning electron microscope (SEM) image (a, b) of the nickel nanosheet array precursor prepared in Example 1 of the present invention;

Figures 1-2 are scanning electron microscope images (a-b) of the tungsten (15 mg) doped nickel nanosheet array prepared in Example 1 of the present invention;

Figure 2-1 is a scanning electron microscope image (a, b) of the nickel phosphide nanosheet array prepared in Example 1 of the present invention;

Figure 2-2 is a scanning electron microscope image (a, b) and a transmission electron microscope image (c) of the tungsten (15 mg) doped nickel phosphide nanosheet array prepared in Example 1 of the present invention;

Figure 2-3 is an element distribution diagram of the W-Ni ₂ P catalyst prepared in Example 1 of the present invention;

Figures 2-4 are X-ray diffraction patterns (XRD) of W-Ni ₂ P and Ni ₂ P catalysts prepared in Example 1 of the present invention;

Figure 3-1 shows the HER linear scan voltammetry curve (a) and the corresponding Tafel slope value diagram (b) of the catalyst prepared in Example 1 of the present invention in 1.0M KOH electrolyte;

Figure 3-2 shows the cyclic voltammetry curve (a) of the W-Ni ₂ P catalyst prepared in Example 1 of the present invention at different sweep speeds; (b) shows the current density difference of the catalyst at a reversible hydrogen potential of 0.924V and The relationship curve of different scanning speeds;

Figure 3-3 shows the electrochemical impedance spectra of different catalysts;

Figure 3-4 shows the HER stability diagram of W-Ni ₂ P electrode;

Figure 4-1 is a linear sweep voltammogram of the catalyst W-Ni ₂ P prepared in Example 1 of the present invention in a 1.0M potassium hydroxide electrolyte and an electrolyte containing 25mM benzylamine;

Figure 4-2 shows the linear sweep voltammogram (a) and Tafel slope plot (b) of different catalysts in the oxidation of benzylamine;

Figure 4-3(a) and BAOR stability diagram of W-Ni ₂ P electrode;

Figure 4-4 shows the hydrogen nuclear magnetic spectrum (ab) and carbon nuclear magnetic spectrum (c) of the W-Ni ₂ P benzylamine electrolysis product of the catalyst prepared in Example 1 of the present invention;

Figure 5 shows the reaction path of the oxidation of benzylamine to benzonitrile in alkaline medium;

Figure 6 is the standard curve of maleic acid calibrated to benzonitrile;

Figure 7-1 is a scanning electron microscope image (a, b) of the tungsten (10 mg) doped nickel phosphide nanosheet array prepared in Example 1 of the present invention;

Figure 7-2 is a scanning electron microscope image (a, b) of the tungsten (20 mg) doped nickel phosphide nanosheet array prepared in Example 1 of the present invention;

Figure 7-3 is a performance comparison chart of HER (a) and BAOR (b) of nickel phosphide nanosheet arrays with different tungsten doping amounts prepared in Example 1 of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention and provides detailed implementation modes and specific operating procedures. However, the protection scope of the present invention is not limited to the following embodiments.

In the following embodiments or examples, nickel nitrate hexahydrate, ammonium fluoride, urea, ammonium metatungstate, and ethanol were purchased from Shanghai McLean Biochemical Technology Co., Ltd., and the remaining unspecified raw material products or processing technologies are shown. All are conventional commercially available products or conventional processing techniques in this field.

Electrochemical data were collected by CHI760E (Shanghai Chenhua).

Example 1:

Precursor tungsten-doped nickel hydroxide, preparation of nickel hydroxide:

Weigh 2mmol nickel nitrate hexahydrate, 6mmol ammonium fluoride, 10mmol urea and 15mg ammonium metatungstate and dissolve it in 30mL deionized water to form a uniform mixed solution. Add this solution to the reaction kettle containing clean nickel foam, 120°C. After 6 hours of hydrothermal reaction, the tungsten-doped nickel single metal precursor loaded on the nickel foam can be obtained, which can be dried in a 60°C vacuum drying oven for later use. Similarly, when ammonium metatungstate is not added in the above scheme, what is synthesized in the hydrothermal process is a nickel single metal precursor without tungsten doped supported on nickel foam.

Preparation of W-doped nickel phosphide bifunctional catalyst and nickel phosphide catalyst:

The tungsten-doped nickel precursor and the tungsten-undoped nickel precursor prepared above were phosphated in an argon atmosphere (300 mg sodium hypophosphite was added upstream) to obtain W-Ni ₂ P/NF bifunctional Electrocatalyst and comparative sample Ni ₂ P catalyst, in which the phosphating temperature is 350°C, the phosphating time is 2h, and the heating rate is 5°C/min.

Figure 1-1 shows the scanning electron microscope image of the nickel single metal precursor. It can be seen from the figure that the nickel precursor is evenly loaded on the surface of the nickel foam, showing a two-dimensional flake morphology and a smooth surface. Figure 1-2 shows the scanning electron microscope image of the tungsten-doped nickel single metal precursor. It can be seen that it also shows a regular nanosheet morphology. Compared with the undoped nickel single metal, the nanosheets are thinner and smaller. .

Figure 2-1 shows the morphology characterization of Ni ₂ P/NF. It can be seen that it retains the structure of the precursor nanosheets and the surface becomes rough; Figure 2-2 shows the scanning electron microscope and image of W-Ni ₂ P/NF. The transmission electron microscope image also retains the structure of the precursor nanosheets, and the surface becomes rough. Compared with Ni ₂ P/NF, the nanosheets are smaller and thinner. Figure 2-3 shows the element distribution diagram of W-Ni ₂ P/NF, showing that the product is mainly composed of three elements: Ni, P and W. Figure 2-4 shows the X-ray diffraction patterns of W-Ni ₂ P/NF and Ni ₂ P/NF, indicating that the sample contains two components: elemental nickel and nickel phosphide.

Test method for the preparation of W-Ni ₂ P/NF as a bifunctional electrocatalyst

Take the final product W-Ni ₂ P catalyst obtained in Example 1 as the HER and BAOR catalyst: the reaction system is a three-electrode system, the nickel foam supporting the W-Ni ₂ P catalyst is used as the working electrode, the graphite rod is the counter electrode, and the mercury/ Mercury oxide is the reference potential. HER and OER tests were performed in 1.0M KOH solution. BAOR testing was performed in 1.0 M KOH solution containing 25mM BA. The scanning speed of the linear sweep voltammetry curve is 5mV s ^-1 . Electrochemical impedance spectroscopy (EIS) measurements were performed in the frequency range from 1MHz to 0.01Hz with an amplitude of 5mV. The Tafel slope is obtained from the LSV plot using a linear fit applied to the points in the Tafel region. The electric double layer capacitance (Cdl) of various samples was calculated by CV at different scan rates in the potential range from 0.4V to 0.6V (vs. RHE). Catalyst stability was evaluated using galvanostatic chronopotentiometry.

Electrolytic product detection method

Long-term electrolysis experiments for the oxidation of benzylamine were performed in a three-electrode system at room temperature. The electrolyte is 25mM BA solution. After the electrolysis is completed, the electrolyte solution is collected and then analyzed by a nuclear magnetic resonance (NMR) spectrometer. Specifically, 500 μL of electrolyte solution was added to 100 μL of D ₂ O, with maleic acid as the internal standard.

Evaluation of HER performance of W-Ni ₂ P/NF catalyst

As shown in Figure 3-1, compared to the three catalysts Ni LDH, W-Ni LDH, and Ni ₂ P, the synthesized W-Ni ₂ P/NF electrode exhibits greater current density and lower overpotential. , Figure b shows the corresponding Tafel slopes of different catalysts. It can be seen from the figure that W-Ni ₂ P/NF has a smaller Tafel slope value, only 74.1mV dec ^-1 , which shows that the prepared The W-Ni ₂ P/NF catalyst has faster hydrogen production kinetics.

Figure 3-2 shows the cyclic voltammetry curves of the catalyst at different scan rates. One-half of the difference between the oxidation current and the reduction current at 0.924V is selected as the capacitive current. Taking the scan rate as the abscissa and the capacitor current at different scan rates as the ordinate, the capacitor current is proportional to the scan rate. The slope of this line is the double electric layer capacitance of the material, and the electrochemically active area is related to the double electric layer. Proportional to the capacitance. The electric double layer capacitance value of W-Ni ₂ P/NF is 37.6mF cm ^-2 , indicating that it has more active sites for hydrogen production.

Figure 3-3 The electrochemical impedance spectrum shows that the W-Ni ₂ P/NF catalyst has the smallest semicircle diameter and steeper slope, confirming its faster charge transfer rate, lower electrode/electrolyte interface resistance and faster Mass diffusion. Figure 3-4 shows that the W-Ni ₂ P/NF catalyst also has good hydrogen production stability.

W-Ni ₂ P catalyst BAOR performance evaluation

Figure 4-1 shows the linear sweep voltammetry curves of OER and BAOR of W-Ni ₂ P/NF electrode. It can be seen from the figure that compared to OER, W-Ni ₂ P/NF has a lower effect on BAOR. Starting oxidation potential.

Panel a in Figure 4-2 shows the linear sweep voltammetry curves of BAOR of different catalysts. It can be seen that the W-Ni ₂ P/NF catalyst exhibits a lower initial oxidation potential and higher catalytic activity. Figure b shows the corresponding Tafel slopes of different catalysts. It can be seen from the figure that W-Ni ₂ P/NF has a smaller Tafel slope value, only 55.7mV dec ^-1 , which shows that the prepared W-Ni ₂ P/NF catalyst has faster benzylamine oxidation kinetics.

Figure 4-3 shows that the W-Ni ₂ P/NF catalyst has good stability for the oxidation of benzylamine.

Figure ab in Figure 4-4 shows the hydrogen nuclear magnetic spectrum of the product collected after the W-Ni ₂ P/NF catalyst electrolyzed benzylamine for a long time. Figure c shows the carbon nuclear magnetic spectrum, which proves the generation of benzonitrile.

Figure 5 shows the possible reaction pathway for the oxidation of benzonitrile by benzylamine in alkaline medium. First, the formation of benzonitrile begins with the breaking of the carbon-hydrogen bond on _-CH2- and the nitrogen-hydrogen bond on _-NH2 , forming C≡N.

Figure 6 is the standard curve of maleic acid calibrated to benzonitrile.

Effect of the amount of ammonium metatungstate on W-Ni ₂ P catalyst

Figures 7-1 and 7-2 show that the doping level of W-Ni ₂ P can be easily adjusted by changing the amount of ammonium metatungstate. However, as the W doping amount increases, the nanosheet structure of W-Ni ₂ P is obviously damaged. Therefore, introducing an appropriate amount of W is important to maintain the active surface area with fine nanostructures.

Figure 7-3 shows that HER and BAOR with a tungsten doping amount of 20 mg have the best performance.

Example 2:

Compared with Example 1, most of them are the same, except that in this example, the addition amounts of the metal precursors nickel salt, urea, ammonium fluoride, and ammonium metatungstate are adjusted to 1 mmol, 5 mmol, 8 mmol, and 10 mg respectively.

Example 3:

Compared with Example 1, most of them are the same, except that in this example, the addition amounts of the metal precursors nickel salt, urea, ammonium fluoride, and ammonium metatungstate are adjusted to 3 mmol, 7 mmol, 12 mmol, and 20 mg respectively.

Example 4:

Compared with Example 1, most of them are the same, except that in this example, the temperature of the hydrothermal reaction is 110°C and the time is 7 hours.

Example 5:

Compared with Example 1, most of them are the same, except that in this example, the temperature of the hydrothermal reaction is 130°C and the time is 5 hours.

Example 6:

Compared with Example 1, most of them are the same, except that in this example, the temperature of high-temperature phosphating is 320°C and the time is 3 hours.

Example 7:

Compared with Example 1, most of them are the same, except that in this example, the temperature of high-temperature phosphating is 380°C and the time is 1 hour.

The above description of the embodiments is to facilitate those of ordinary skill in the technical field to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without inventive efforts. Therefore, the present invention is not limited to the above embodiments. Based on the disclosure of the present invention, improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims (10)

1. The preparation method of the tungsten-doped nickel phosphide nanosheet array material is characterized by comprising the following steps of:

(1) Dispersing metal precursor nickel salt, urea, ammonium fluoride and ammonium metatungstate solution in deionized water to form a uniform solution, transferring the uniform solution into a reaction kettle containing foam nickel, and carrying out hydrothermal reaction to obtain a tungsten-doped nickel single metal precursor loaded on the foam nickel;

(2) And (3) placing the tungsten-doped nickel single-metal precursor loaded on the foam nickel in an argon atmosphere with sodium hypophosphite at high temperature for phosphating to obtain a tungsten-doped nickel phosphide nanosheet array material, namely the target product.

2. The method of claim 1, wherein in step (1), the metal precursor nickel salt is nickel nitrate hexahydrate.

3. The method for preparing the tungsten-doped nickel phosphide nanosheet array material as claimed in claim 1, wherein in the step (1), the addition amount ratio of metal precursor nickel salt, urea, ammonium fluoride and ammonium metatungstate is (1-3) mmol: (5-7) mmol: (8-12) mmol: (10-20) mg.

4. The method for preparing the tungsten-doped nickel phosphide nano-sheet array material according to claim 1, wherein in the step (1), the hydrothermal reaction temperature is 110-130 ℃ and the time is 5-7h.

5. The method for preparing a tungsten-doped nickel phosphide nanosheet array material as claimed in claim 1, wherein in the step (1), the foam nickel is subjected to cleaning treatment before being placed into a reaction kettle.

6. The method for preparing the tungsten-doped nickel phosphide nano-sheet array material according to claim 1, wherein in the step (2), the high-temperature phosphating temperature is 320-380 ℃ and the time is 1-3h.

7. The method for preparing a tungsten-doped nickel phosphide nanosheet array material as claimed in claim 6, wherein in step (2), the temperature rising rate in the high-temperature phosphating process is 5 ℃/min.

8. A tungsten doped nickel phosphide nanosheet array material prepared by the preparation method as claimed in any one of claims 1-7.

9. Use of a tungsten doped nickel phosphide nanoplatelet array material according to claim 8 as a bifunctional electrocatalyst in HER and BAOR under alkaline conditions.

10. The use of a tungsten doped nickel phosphide nanoplatelet array material according to claim 9 for selective oxidation of benzylamine to form value added benzonitrile.