CN109046408B - A kind of composite hydrogen evolution electrocatalytic material and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the field of hydrogen production by water electrolysis, and particularly relates to a preparation method and application of a composite hydrogen evolution electro-catalytic material. The method for preparing the composite hydrogen evolution electro-catalysis material specifically comprises the following steps: dispersing polyvinylpyrrolidone and cobalt nitrate hexahydrate in deionized water, and stirring to obtain a mixed solution; performing water bath reaction, calcining the product in a tubular furnace, naturally cooling to room temperature, and washing to obtain a cobalt simple substance @ three-dimensional nitrogen-doped porous carbon material; and mixing the prepared cobalt simple substance @ three-dimensional nitrogen-doped porous carbon material with a phosphorus source, calcining in a tubular furnace, washing and drying the obtained product to obtain the cobalt phosphide @ three-dimensional nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material. The invention adopts a two-step synthesis method, and the preparation method is easy to operate, simple and feasible; the used raw materials have rich reserves and low price. The composite hydrogen evolution electro-catalysis material prepared by the invention has a three-dimensional porous structure and has excellent electro-catalysis hydrogen evolution performance under acidic, neutral and alkaline conditions.

Description

A kind of composite hydrogen evolution electrocatalytic material and preparation method and application thereof

technical field

The invention belongs to the field of hydrogen production by electrolysis, in particular to a preparation method and application of a composite hydrogen evolution electrocatalytic material, in particular to a cobalt phosphide@three-dimensional nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material and its preparation method and application.

Background technique

With the increasing energy crisis and environmental pollution, developing green energy and solving the problems of environmental pollution and energy crisis are the primary choices to maintain sustainable development. The main energy source in my country is non-renewable fossil fuels. The energy structure is single and the carbon dioxide released during the combustion of fossil fuels is also the culprit of the greenhouse effect. The current renewable energy sources mainly include wind energy, solar energy, biomass energy, and hydrogen energy. Among them, hydrogen energy is a recognized ideal fuel, and its combustion value is three times that of petroleum. The most important thing is that the combustion product of hydrogen is only water, which is an efficient and clean energy source. Therefore, the development of hydrogen energy is the most effective way to solve the current problem.

At present, the most efficient electrocatalytic hydrogen evolution reaction (HER) catalyst is still the precious metal Pt. Due to the scarcity of precious metal reserves and high price, it is still unable to be produced and applied on a large scale. Therefore, the development of non-precious metal HER catalysts that can replace the noble metal Pt is an effective way to solve this problem. Cobalt phosphide has been proven to be a highly active HER catalyst, and it is suitable for large-scale production applications because of its abundant reserves and low cost. It is an effective strategy to prevent their agglomeration when combined with a suitable carbon support. For example, commonly used carbon supports include graphene and carbon nanotubes. Although graphene and carbon nanotubes can anchor cobalt phosphide nanoparticles to prevent their agglomeration, the preparation process of graphene requires the use of strong oxidants, such as concentrated sulfuric acid, potassium permanganate, etc., which takes a long time, and the preparation conditions are harsh and dangerous. The graphene of carbon nanotubes is also difficult to disperse, and these shortcomings limit the general application of graphene; the preparation process of carbon nanotubes is complicated, and it is difficult to obtain uniform carbon nanotubes. Therefore, using an appropriate method to load nanoparticles with HER catalytic activity on an easily prepared carbon support is an effective way to improve the easy agglomeration of monomers and solve the shortcomings of carbon supports such as graphene.

At present, some cobalt phosphide and carbon support composite catalysts have cobalt phosphide nanoparticles with large size, which leads to insufficient exposure of active sites, high overpotential for hydrogen evolution in electrolyzed water, and waste of electric energy; poor stability and cannot work stably for a long time , resulting in low HER efficiency; some can only achieve good hydrogen evolution activity under relatively simple conditions such as acidic or basic conditions, and cannot work in a full pH aqueous solution environment, which limits the application range of HER catalysts. In addition, different carbon materials have special effects, such as the doping of nitrogen atoms, which can lead to carbon material defects and generate more active sites, thereby enhancing its catalytic activity.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the technical defects existing in the prior art, such as: monomer cobalt phosphide is easy to agglomerate, which is not conducive to the full exposure of active sites; the graphene preparation conditions used are harsh and dangerous, and it is difficult to disperse It is difficult to obtain uniform carbon nanotubes; some catalysts composited with cobalt phosphide and carbon support have large cobalt phosphide nanoparticles, resulting in insufficient exposure of active sites, high overpotential for hydrogen evolution from electrolyzed water, and waste of electrical energy. Stability, poor HER, low efficiency and other problems, the present invention provides a preparation method of a composite hydrogen evolution electrocatalytic material.

Specifically, the technical solution adopted in the present invention is:

(1) Preparation of metal carbon precursor:

Disperse polyvinylpyrrolidone and cobalt nitrate hexahydrate in deionized water, stir to obtain a mixed solution; react in a water bath to obtain a product; after calcining the product in a tube furnace, naturally cool to room temperature, and wash to obtain cobalt element@3D Nitrogen-doped porous carbon materials;

(2) Phosphating:

The cobalt element @ three-dimensional nitrogen-doped porous carbon material in step (1) is mixed with a phosphorus source, calcined in a tube furnace, and the obtained product is washed and dried to obtain cobalt phosphide@ three-dimensional nitrogen-doped porous carbon composite hydrogen evolution Electrocatalytic materials.

In step (1), the mass ratio of cobalt nitrate hexahydrate to polyvinylpyrrolidone is 0.8-1.4; the stirring time is 10min-30min; the temperature of the water bath is 65°C-75°C, and the time of the water bath is 5h -7h; the calcination temperature is 750°C-800°C, the calcination time is 40min-50min, and the heating rate is 5°C·min ^-1 ;

In step (2), the phosphorus source is red phosphorus; the mass ratio of the cobalt element@3D nitrogen-doped porous carbon material to the phosphorus source is 0.5-0.7; the calcination temperature is 500°C-600°C, and the calcination time for 1.5h-2.5h, the heating rate is 5°C·min ^-1 ; the drying temperature is 80°C.

The present invention also provides a composite electrocatalytic material for hydrogen evolution, which is in the form of a three-dimensional porous carbon nanosheet network structure and has a large specific surface area; cobalt phosphide nanoparticles are evenly embedded in the carbon nanosheets, and the cobalt phosphide particle size is 5- 10nm.

The present invention also provides the use of a composite electrocatalytic material for hydrogen evolution, wherein the composite electrocatalytic material for hydrogen evolution is used for electrolysis of water for hydrogen evolution.

Compared with the prior art, the beneficial effects of the present invention are embodied as follows:

(1) The present invention uses polyvinylpyrrolidone (PVP) as the carbon source and cobalt nitrate hexahydrate as the cobalt source, and the raw materials used are abundant in reserves and low in price. Here, polyvinylpyrrolidone can act as a dispersant to make the dispersion of cobalt nitrate in the aqueous solution more uniform, so that the reduced cobalt has smaller size and uniform particle size. At high temperature, the gas generated by the decomposition of cobalt nitrate leads to the formation of three-dimensional porous carbon, and at the same time, cobalt ions are reduced to cobalt and embedded in carbon nanosheets, which saves some research on the process of first preparing carbon carriers, and finally obtains phosphorus The particle size of cobalt oxide is only 5-10 nm, which exposes more active sites.

(2) In addition, the present invention adopts a two-step synthesis method. The first step is to prepare cobalt element @ three-dimensional nitrogen-doped porous carbon material, and the second step is to prepare cobalt phosphide @ three-dimensional nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material. The method is easy to operate, simple and feasible. In the preparation process of the present invention, the introduction of three-dimensional porous carbon increases the specific surface area of the composite and also improves the electrical conductivity of the composite, that is, exposing more active sites and accelerating the electron transfer rate, so the composite The electrocatalytic hydrogen evolution performance of the compound is also greatly enhanced.

(3) Compared with the catalyst materials supported by graphene and carbon nanotubes, which can only be prepared in small batches, the catalyst material of the present invention is easy to produce in large quantities, and the cobalt phosphide ions embedded in the carbon nanosheets are wrapped by the surrounding carbon, avoiding the need for electrolytes. The solution is in direct contact, which is more stable than the catalyst exposed on the surface of the carbon support. The conductivity of carbon materials doped with nitrogen atoms will also be further improved, thereby improving the hydrogen evolution efficiency.

(4) The cobalt phosphide@three-dimensional nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material prepared by the present invention has small cobalt phosphide nanoparticles, about 10 nm, and is uniformly dispersed on the carbon nanosheets; The multi-channel transport of electrons and ions in the electrolyte solution, and the doping of nitrogen can optimize the electronic structure of carbon materials and further enhance the electrocatalytic activity; it has excellent catalytic performance under acidic, neutral and alkaline conditions. The composite hydrogen evolution electrocatalytic material prepared by the invention has good electrocatalytic hydrogen evolution performance in the whole pH range. In 0.5 MH ₂ SO ₄ , 1.0 M PBS and 1.0 M KOH, when the current density reaches 10 mA cm ^-2 , the required hydrogen evolution overpotentials are 131 mV, 300 mV and 180 mV, respectively, and the corresponding Tafel slopes are 58 mV dec ^-1 , 71 mV dec ^-1 and 65 mV dec ^-1 .

Description of drawings

Fig. 1 is the XRD diffractogram of cobalt phosphide@three-dimensional nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material of the present invention;

2 is a scanning electron microscope (SEM) image of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material of the present invention;

3 is a transmission electron microscope (TEM) image of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material of the present invention;

Figure 4 is the electrocatalytic hydrogen evolution curve of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material in 0.5 MH ₂ SO ₄ ;

Figure 5 is the Tafel slope diagram of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material in 0.5 MH ₂ SO ₄ ;

Figure 6 shows the electrocatalytic hydrogen evolution curves of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic materials in 1.0 M KOH;

Figure 7 is the Tafel slope plot of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material in 1.0 M KOH;

Figure 8 is the electrocatalytic hydrogen evolution curve of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material in 1.0 M PBS;

Figure 9 shows the Tafel slope plot of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material in 1.0 M PBS.

Detailed ways

Below in conjunction with specific example, the present invention is further elaborated:

Example 1:

(1) Preparation of metal carbon precursor:

5 g of polyvinylpyrrolidone was dissolved in 150 ml of deionized water containing 4 g of Co(NO ₃ ) ₂ ·6H ₂ O, and then stirred for 10 minutes to obtain a mixed solution; then the mixed solution was transferred to a water bath and heated at 65 °C The product was obtained in a water bath for 5 hours; then, the product was placed in a porcelain crucible, calcined in a tube furnace at 750 °C for 40 min, and the heating rate was 5 °C·min ^-1 . After naturally cooling to room temperature, the obtained product was collected and deionized water was used. and ethanol were washed three times, respectively, to obtain cobalt element@3D nitrogen-doped porous carbon material (Co@3D-NPC composite material).

(2) Phosphating:

0.5 g of the Co@3D-NPC composite obtained in step (1) and 1 g of red phosphorus powder were placed in a ceramic boat, and the red phosphorus powder was placed on the upstream side; then the ceramic boat was heated in a quartz tube at 500 °C For 1.5 h, under nitrogen flow protection, the heating rate was 5 °C·min ^-1 ; finally, the furnace was cooled to room temperature, and the obtained black product was washed three times with deionized water and ethanol each, and dried at 80 °C to obtain Cobalt phosphide@3D nitrogen-doped porous carbon composite electrocatalytic material for hydrogen evolution (CoP@3D-NPC composite).

Example 2:

(1) Preparation of metal carbon precursors

5 g of polyvinylpyrrolidone was dissolved in 150 ml of deionized water containing 6 g of Co(NO ₃ ) ₂ ·6H ₂ O, and then stirred for 20 minutes to obtain a mixed solution; then the mixed solution was transferred to a water bath and heated at 70 °C The product was obtained in a water bath for 6 hours; then the product was placed in a porcelain crucible, calcined in a tube furnace at 775 °C for 45 min, and the heating rate was 5 °C·min ^-1 . After naturally cooling to room temperature, the obtained product was collected and deionized water was used. and ethanol were washed three times, respectively, to obtain cobalt element@3D nitrogen-doped porous carbon material (Co@3D-NPC composite material).

(2) Phosphating:

Place 0.6 g of the Co@3D-NPC composite obtained in step (1) and 1 g of red phosphorus powder in a ceramic boat, and place the red phosphorus powder on the upstream side; then heat the ceramic boat in a quartz tube at 550 °C 2 h, protected under nitrogen flow, the heating rate was 5 ℃·min ^-1 ; finally, the furnace was cooled to room temperature, and the obtained black product was washed 3 times with deionized water and ethanol, and dried at 80 ℃ to obtain phosphorus Cobalt oxide@3D nitrogen-doped porous carbon composite electrocatalytic material for hydrogen evolution (CoP@3D-NPC composite).

Example 3:

(1) Preparation of metal carbon precursor:

5 g of polyvinylpyrrolidone was dissolved in 150 ml of deionized water containing 7 g of Co(NO ₃ ) ₂ ·6H ₂ O, and then stirred for 30 minutes to obtain a mixed solution; then the mixed solution was transferred to a water bath and heated at 75 °C The product was obtained in a water bath for 7 hours; then the product was placed in a porcelain crucible, calcined in a tube furnace at 800 °C for 50 min, and the heating rate was 5 °C·min ^-1 , and after naturally cooling to room temperature, the obtained product was collected and deionized water was used. and ethanol were washed three times, respectively, to obtain cobalt element@3D nitrogen-doped porous carbon material (Co@3D-NPC composite material).

(2) Phosphating:

0.7 g of the Co@3D-NPC composite obtained in step (1) and 1 g of red phosphorus powder were placed in a ceramic boat, and the red phosphorus powder was placed on the upstream side; then the ceramic boat was heated in a quartz tube at 600 °C For 2.5 h, under nitrogen flow protection, the heating rate was 5 ℃·min ^-1 ; finally, the furnace was cooled to room temperature, and the obtained black product was washed three times with deionized water and ethanol, and dried at 80 ℃ to obtain phosphorus Cobalt oxide@3D nitrogen-doped porous carbon composite electrocatalytic material for hydrogen evolution (CoP@3D-NPC composite).

Electrocatalytic hydrogen evolution performance test:

The electrocatalytic hydrogen evolution performance of the Co@3D-NPC composites prepared in Examples 1-3 was tested by a three-electrode system. The working electrode was prepared by the drop coating method. The specific process was as follows: Weigh 5 mg of the sample into a 2 mL centrifuge tube, add 0.98 mL of ethanol and 0.02 mL of a 5 % Nafion solution, and sonicate for 30 min to form a catalyst solution. A glassy carbon electrode with a diameter of 5 mm was used as the working electrode, which was polished and smoothed into a mirror surface. 0.01 ml of catalyst solution was drop-coated on the working electrode, and the electrochemical tests were carried out after drying naturally. The test solutions were 0.5 MH ₂ SO ₄ , 1.0 M KOH, 1.0 MPBS.

In 0.5MH ₂ SO ₄ , 1.0MPBS and 1.0MKOH, when the current density reaches 10mAcm ^-2 , the required hydrogen evolution overpotentials are 131mV, 300 mV and 180 mV, respectively, and the corresponding Tafel slopes are only 58 mV dec ^-1 , 71 mV dec ^-1 and 65 mV dec ^-1 .

1 is the XRD diffraction pattern of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) of the present invention, specifically the cobalt phosphide@3D nitrogen-doped porous carbon obtained in Example 2 The XRD pattern of the 3D nitrogen-doped porous carbon shows that the main diffraction peaks are consistent with the CoP phase standard card JCPDS: 29-0497, indicating the successful preparation of cobalt phosphide@3D nitrogen-doped porous carbon.

Figure 2 is a scanning electron microscope image of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material of the present invention; as can be seen from Figure 2, it can be seen that the cobalt phosphide@3D nitrogen-doped porous carbon sample is a three-dimensional porous carbon The nanosheet network structure has a large specific surface area.

3 is a transmission electron microscope image of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material of the present invention, it can be seen that CoP nanoparticles are evenly embedded in carbon nanosheets, and the particle size of cobalt phosphide is 5-10nm , the smaller particle size is conducive to the full exposure of active sites, thereby improving the electrocatalytic activity.

Fig. 4 shows the electrocatalytic hydrogen evolution curve of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) in 0.5 MH ₂ SO ₄ ; it can be seen from Fig. 4 , when the current density reaches 10 mA cm ^-2 , the required hydrogen evolution overpotential is only 131 mV, respectively.

Figure 5 is the Tafel slope diagram of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) in 0.5 MH ₂ SO ₄ ; it can be seen from Figure 5 out, the corresponding Tafel slope is 58 mV dec ^-1 .

Figure 6 shows the hydrogen evolution curves of electrolytic water electrolysis of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) in 1.0 MKOH, when the current density reaches 10 mA ^{cm- 2} , the required hydrogen evolution overpotentials are only 180 mV, respectively.

Figure 7 shows the Tafel slope diagram of the cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) in 1.0 M KOH; it can be seen from Figure 7 that, The corresponding Tafel slope is 65 mV dec ^-1 .

Figure 8 shows the hydrogen evolution curve of electrolytic water electrolysis of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) in 1.0 MPBS, when the current density reaches 10 mA cm ^-2 , the required hydrogen evolution overpotential is only 300mV, respectively.

Figure 9 shows the Tafel slope diagram of cobalt phosphide@3D nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material (cobalt phosphide@3D nitrogen-doped porous carbon) in 1.0MPBS, the corresponding Tafel slope is 71 mV dec ^-1 .

The composite hydrogen evolution electrocatalytic material prepared by the invention has good electrocatalytic _hydrogen evolution performance in the whole pH range, that is, under acidic, neutral and alkaline conditions _. In KOH, when the current density reaches 10 mA cm ^-2 , the required hydrogen evolution overpotentials are 131 mV, 300 mV and 180 mV, respectively, and the corresponding Tafel slopes are 58 mV dec ^-1 , 71 mV dec ^-1 and 65 mV dec ^-1 . In summary, the preparation method of the present invention greatly reduces the hydrogen evolution overpotential of the prepared cobalt phosphide@3D nitrogen-doped porous carbon, improves the stability and electrolysis efficiency, and solves the problem that some catalysts can only work in a single aqueous solution environment. question.

Claims (8)

1. The preparation method of the composite hydrogen evolution electrocatalytic material is characterized by comprising the following steps of:

(1) preparing a metal carbon precursor:

dispersing polyvinylpyrrolidone and cobalt nitrate hexahydrate in deionized water, and stirring to obtain a mixed solution; performing water bath reaction to obtain a product; placing the product in a tubular furnace for calcining, naturally cooling to room temperature, and washing to obtain a cobalt simple substance @ three-dimensional nitrogen-doped porous carbon material;

(2) phosphorization:

mixing the cobalt simple substance @ three-dimensional nitrogen-doped porous carbon material obtained in the step (1) with a phosphorus source, placing the mixture in a tubular furnace for calcination, and washing and drying the obtained product to obtain the cobalt phosphide @ three-dimensional nitrogen-doped porous carbon composite hydrogen evolution electrocatalytic material.

2. The method for preparing the composite hydrogen evolution electrocatalytic material as set forth in claim 1, wherein in the step (1), the mass ratio of the cobalt nitrate hexahydrate to the polyvinylpyrrolidone is 0.8-1.4.

3. The method for preparing the composite hydrogen evolution electrocatalytic material as set forth in claim 1, wherein in the step (1), the stirring time is 10-30 min; the temperature of the water bath is 65-75 ℃, and the time of the water bath is 5-7 h.

4. The method for preparing the composite hydrogen evolution electro-catalytic material according to claim 1, wherein in the step (1), the calcination temperature is 750-800 ℃, the calcination time is 40-50 min, and the temperature rise rate is 5 ℃ min^-1。

5. The method for preparing the composite hydrogen evolution electrocatalytic material as set forth in claim 1, wherein in the step (2), the phosphorus source is red phosphorus.

6. The preparation method of the composite hydrogen evolution electrocatalytic material as claimed in claim 1, wherein in the step (2), the mass ratio of the cobalt simple substance @ three-dimensional nitrogen-doped porous carbon material to the phosphorus source is 0.5-0.7.

7. The method for preparing the composite hydrogen evolution electro-catalytic material according to claim 1, wherein in the step (2), the calcination temperature is 500-600 ℃, the calcination time is 1.5-2.5 h, and the temperature rise rate is 5 ℃ min^-1。

8. The method for preparing a composite hydrogen evolution electrocatalytic material as set forth in claim 1, wherein the drying temperature in the step (2) is 80 ℃.

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