CN111282588A - Catalyst for hydrogen evolution by electrolyzing water and preparation method and application thereof - Google Patents

Abstract

The invention discloses a hydrogen evolution catalyst for electrolysis water and a preparation method thereof. The hydrogen evolution catalyst is molybdenum carbide supported on a carbon-nitrogen-doped carbon composite carrier, and the preparation method includes the following steps: firstly, a precursor is obtained by in-situ growth of molybdenum-doped polyaniline on the carbon carrier by a chemical oxidation method, and the precursor is After being washed and dried, the catalyst was obtained by high temperature treatment under nitrogen protection. The reagents used in the invention have low price and short production process, and electrochemical tests show that the obtained catalyst has a good effect of catalyzing hydrogen evolution.

Description

A kind of electrolysis water hydrogen evolution catalyst and preparation method and application thereof

technical field

The invention belongs to the field of electrocatalysis, and in particular relates to a carbon-nitrogen- _doped carbon (NC)-based molybdenum carbide (Mo2C) composite material and a preparation method thereof.

Background technique

In today's society, the energy crisis and environmental pollution have become increasingly severe, threatening the survival and development of human beings. Hydrogen energy is a very important energy source, which is considered as an ideal energy carrier for sustainable energy storage and an alternative to fossil fuels due to its high energy density and environmental friendliness. At present, the production of hydrogen depends on the fossil fuel industry, so it also faces many problems, such as low hydrogen purity and high cost; using electric current to split water to generate hydrogen and oxygen is a very effective hydrogen production method, and the production cost is relatively high. low, the hydrogen produced has high purity.

Hydrogen production by electrolysis of water is considered to be an efficient route for large-scale industrial hydrogen production. Among them, noble metals show extremely excellent catalytic activity. For example, Pt-based catalysts are currently recognized as the best catalysts for water electrolysis and hydrogen production. However, due to their limited reserves and high prices, noble metals cannot be widely used in large-scale applications. Molybdenum carbide is an efficient hydrogen evolution catalyst that is considered to be a substitute for Pt-based catalysts. In order to improve electrical conductivity and improve mass transfer, hydrogen evolution catalysts are often compounded with various carbon supports to improve catalytic performance.

SUMMARY OF THE INVENTION

The invention provides a new preparation method for preparing carbon-nitrogen doped carbon-based molybdenum carbide material, and the preparation method is simple and has good catalytic effect in the hydrogen evolution of water electrolysis.

For achieving the above object, the present invention provides the following technical solutions:

One aspect of the present invention provides a method for preparing a hydrogen evolution catalyst for electrolysis of water, the method comprising the steps of:

Step 1: The carbon carrier is oxidized, washed, and dried in a vacuum drying oven;

Step 2: Dissolve the carbon carrier and ammonium molybdate treated in step 1 in deionized water, add a certain amount of aniline, and stir in an ice bath until the ammonium molybdate is dissolved and kept at a constant temperature;

Step 3: configure the HCl solution of ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ with a certain concentration, add it to the solution of step 2 and continue stirring;

Step 4: the mixed solution becomes dark green, the lower layer is centrifuged to remove the precipitate and washed several times, and dried in a vacuum drying oven to obtain a molybdenum-doped carbon-polyaniline precursor;

Step 5: Grind the precursor in Step 4 into powder, put it into a tube furnace, heat treatment in a protective atmosphere and naturally cool to obtain a carbon-nitrogen doped carbon-based molybdenum carbide material.

Based on the above technical solutions, preferably, the carbon material in step 1 is any one of graphite and carbon nanotubes. For the oxidation treatment of graphene, the Hummers oxidation method is used to prepare graphene oxide from graphite. In the oxidation treatment of carbon nanotubes, the carbon nanotubes are refluxed in concentrated nitric acid at 60-70° C. for 3-4 hours, and washed to neutrality.

Based on the above technical solutions, preferably, the drying in steps 1 and 4 refers to drying in a vacuum drying oven at 60-80° C. for 12-14 hours.

Based on the above technical solutions, preferably, the protective gas in step 5 is any one of nitrogen and argon.

Based on the above technical solutions, preferably, the heat treatment in step 5 is to heat up to 750-800° C. at a rate of 3-5° C./min for 3-4 hours.

Another aspect of the present invention provides a hydrogen evolution catalyst for water electrolysis prepared by the above method, characterized in that the catalyst-supported catalyst is a carbon-nitrogen doped carbon composite support, and the supported material is molybdenum carbide. .

Another aspect of the present invention provides an application of the above-mentioned hydrogen evolution catalyst for electrolysis of water, wherein the catalyst is used for the hydrogen evolution reaction of electrolyzed water.

The advantages of the present invention are:

1. The present invention utilizes the coordination of aniline and molybdate ions, and makes them uniformly polymerized on the carbon carrier, which is beneficial to the dispersion of molybdenum elements, avoids the agglomeration in the subsequent high temperature process, exposes more active sites, and improves electrocatalysis. active;

2. The preparation process of the invention is simple, the operation is controllable, the catalytic performance is good, and the invention has the potential of industrial application.

Description of drawings

Fig. 1 is the X-ray diffraction analysis diagram of Mo ₂ C/rGO-NC prepared in Example 1;

Fig. 2 is the X-ray diffraction analysis diagram of Mo ₂ C/NC prepared in Example 3;

3 is an X-ray diffraction analysis diagram of Mo ₂ C/CNTs-NC prepared in Example 2;

4 is a scanning electron microscope image of Mo ₂ C/rGO-NC prepared in Example 1;

5 is a scanning electron microscope image of Mo ₂ C/NC prepared in Example 3;

6 is a scanning electron microscope image of Mo ₂ C/CNTs-NC prepared in Example 2;

Fig. 7 is the EDX element distribution diagram of Mo ₂ C/rGO-NC prepared in Example 1;

Fig. 8 is the EDX element distribution map of Mo ₂ C/NC prepared in Example 3;

Fig. 9 is the EDX element distribution diagram of Mo ₂ C/CNTs-NC prepared in Example 2;

Fig. 10 is the linear sweep voltammogram of embodiment 1, 2, embodiment 3;

FIG. 11 is a Tafel slope diagram of Examples 1, 2, and 3. FIG.

Detailed ways

Example 1

Graphene oxide (GO) was prepared by Hummers method: 1 g of graphite flakes and 1 g of sodium nitrate were put into 50 mL of concentrated sulfuric acid and stirred for 2 h in an ice bath, and 4 g of potassium permanganate powder was slowly added and continuously stirred in an ice bath, and then transferred to 35 The reaction was carried out at a medium temperature in an oil bath for 2 hours, 150 mL of deionized water was added dropwise and the temperature was raised to 95 °C. After the dropwise addition, the product was dispersed in deionized water, and 10 mL of hydrogen peroxide and 100 mL of 10% wt hydrochloric acid were added to stir and centrifuge, and the precipitate was put into dialysis. The bag is dialyzed with deionized water until it does not contain sulfate ions, and finally the product is frozen with liquid nitrogen and dried in a freeze dryer to obtain graphene oxide. Take 30 mg of graphene oxide and 60 mg of ammonium molybdate and dissolve it in 20 mL of deionized water, add 95 mg of aniline dropwise and stir and disperse evenly in an ice bath. The reaction was carried out for 4 hours. The solution turned dark green, centrifuged and washed with deionized water for several times, and dried in a vacuum drying oven at 60°C for 12 h to obtain the molybdenum-doped graphene oxide-polyaniline precursor. The precursor was placed in a porcelain boat, and nitrogen was used as a protective gas in a tube furnace, heated to 800°C at 5°C/min for 3 hours, and then cooled naturally to obtain a Mo ₂ C/rGO-NC catalyst.

Example 2

Surface oxidation treatment of carbon nanotubes (CNTs): 1 g of multi-walled carbon nanotubes was added to 30 mL of concentrated nitric acid and stirred, and refluxed in an oil bath at 60 °C for 3 h. Obtained by drying at 60°C for 12h in a drying oven. Dissolve 30 mg of surface oxidized carbon nanotubes and 60 mg of ammonium molybdate in 20 mL of deionized water, add 95 mg of aniline dropwise and stir to disperse evenly in an ice bath. The reaction in the bath was 4h. The solution turned dark green, centrifuged and washed with deionized water for several times, put into a vacuum drying oven at 60 °C for 12 h to obtain molybdenum-doped carbon nanotube-polyaniline precursor. The precursor was placed in a porcelain boat, and nitrogen was used as a protective gas in a tube furnace. The temperature was raised to 800°C at 5°C/min for 3 hours, and then cooled naturally to obtain a Mo ₂ C/CNTs-NC catalyst.

Example 3

Dissolve 60 mg of ammonium molybdate in 20 mL of deionized water, add 95 mg of aniline dropwise, stir and disperse evenly in an ice bath, add 10 mL of a prepared 0.5 M HCl solution containing 0.4 g of ammonium persulfate dropwise, and react in an ice bath for 4 h. The solution turned dark green, centrifuged and washed several times with deionized water, and then put it into a vacuum drying oven for drying at 60°C for 12 hours to obtain the molybdenum-doped polyaniline precursor. The precursor was put into a porcelain boat, and nitrogen was used as a protective gas in a tube furnace, and the temperature was raised to 800°C at 5°C/min for 3 hours, and then cooled naturally to obtain a Mo ₂ C/NC catalyst. Example 3 followed the same procedure as Example 1 and Example 2, but without adding a carbon support.

It can be seen from Figure 1, Figure 2 and Figure 3 that the diffraction peaks of the catalyst are less obvious, indicating that the molybdenum carbide catalyst has a lower crystallinity, which is beneficial to expose more active sites. _The characteristic peaks of molybdenum carbide can be displayed at 38.0°, 39.6°, 52.3°, 61.9°, and 69.8°, which are assigned to (002), (101), ( 102), (110), (103) crystal planes. The above results show that the preparation method of the present invention is favorable for the formation of more oxygen vacancies.

It can be seen from Figure 4 that the catalyst basically maintains the original morphology of carbon-supported graphene oxide, which is a two-dimensional sheet-like structure, and more holes are conducive to the transport of substances.

It can be seen from FIG. 5 that the molybdenum carbide catalyst synthesized by using polyaniline as a precursor in the present invention has a smaller particle size, which is beneficial for the catalyst to expose more active sites.

It can be seen from Fig. 7, Fig. 8 and Fig. 9 that Mo, C, and N elements are uniformly distributed, indicating that the pyrolysis product of polyaniline is nitrogen-doped carbon.

Electrocatalytic test: 5 mg of catalyst and 80 μL of 5% Nafion solution were dispersed in isopropanol solution and ultrasonicated for 30 min to obtain catalyst slurry. Pipette 10 μL of the catalyst slurry onto a glassy carbon electrode with a diameter of 5 mm, and dry it under an infrared baking lamp to form a thin-film catalyst layer. In a three-electrode system (the glassy carbon electrode is the working electrode, the carbon rod is the counter electrode, the calomel electrode is the reference electrode, and the 0.5M sulfuric acid solution is the electrolyte solution), the linear sweep voltammetry curve is measured, and the test results are shown in Figure 10. The overpotential of the catalyst was tested at 10 mAcm ^-2 . The Tafel curve of each sample can be obtained from the linear sweep voltammetry curve, as shown in Figure 11. The test results are as follows:

sample Overpotential (10mAcm^-2) Tafel slope Example 1 55mV 109mV/dec Example 2 27mV 115mV/dec Example 3 91mV 108mV/dec

It can be seen from the results that in the catalyst obtained by the preparation method of the present invention, the molybdenum carbide has small particle size and low crystallinity, which is conducive to the formation of more oxygen vacancies and is conducive to the reaction; the catalyst prepared by adding carbon nanotubes and graphene oxide as a carbon source carrier Mo ₂ C/CNTs-NC and catalyst Mo ₂ C/rGO-NC exhibited better catalytic hydrogen evolution performance with lower overpotential.

Claims (7)

1. a preparation method of a hydrogen-evolution catalyst for electrolysis of water, is characterized in that, described method comprises the steps: Step 1: The carbon material is oxidized, washed, and dried in vacuum; Step 2: Dissolve the carbon material and ammonium molybdate treated in step 1 in deionized water, add a certain amount of aniline, and stir in an ice bath until the ammonium molybdate is dissolved and kept at a constant temperature; Step 3: prepare a 0.5M HCl solution of 30-40g/L ammonium persulfate, add it into the solution of step 2 and continue stirring for 4-6h to obtain a mixed solution; Step 4: centrifugally washing the mixed solution described in Step 3, and vacuum drying to obtain a molybdenum-doped carbon-polyaniline precursor; Step 5: grinding the molybdenum-doped carbon-polyaniline precursor into powder, heat treatment in a protective atmosphere and natural cooling to obtain the catalyst. 2. the preparation method of hydrogen evolution catalyst for electrolysis of water according to claim 1, is characterized in that, described carbon material is graphite, and described oxidation treatment is that Hummers oxidation method prepares graphene oxide with graphite; Described carbon material is For carbon nanotubes, the oxidation treatment is to reflux and wash carbon nanotubes in concentrated nitric acid at 60° C. to neutrality. 3. The preparation method of a hydrogen evolution catalyst for electrolyzed water according to claim 1, wherein the vacuum drying of the step 1 and the step 4 refers to drying in a vacuum drying oven at 60-80° C. for 12-14 hours. 4. The preparation method of the hydrogen evolution catalyst for electrolysis of water according to claim 3, wherein the protective gas described in the step 5 is any one of nitrogen and argon. 5. The preparation method of a hydrogen evolution catalyst for water electrolysis according to claim 3, wherein the heat treatment described in the step 5 is to heat up to 750 to 800 DEG C for 3 to 4 hours at a rate of 3 to 5 DEG C/min. 6. a hydrogen-evolution catalyst for electrolysis of water prepared by the method of any one of claims 1-5, wherein the catalyst is a supported catalyst, and the carrier is a carbon-nitrogen-doped carbon composite carrier, and a supported material For molybdenum carbide. 7. the application of a hydrogen-evolution catalyst for electrolysis of water according to claim 6, characterized in that the catalyst is used for the hydrogen-evolution reaction of electrolyzed water.

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