CN111282588A

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

Info

Publication number: CN111282588A
Application number: CN201811499603.5A
Authority: CN
Inventors: 邵志刚; 黄河; 唐雪君; 覃博文; 杨丽梦; 秦晓平
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2018-12-09
Filing date: 2018-12-09
Publication date: 2020-06-16

Abstract

The invention discloses a catalyst for hydrogen evolution by water electrolysis and a preparation method thereof. The hydrogen evolution catalyst is molybdenum carbide loaded on a carbon-nitrogen doped carbon composite carrier, and the preparation method comprises the following steps: firstly, growing molybdenum-doped polyaniline in situ on a carbon carrier by a chemical oxidation method to obtain a precursor, washing and drying the precursor, and then carrying out high-temperature treatment under the protection of nitrogen to obtain the catalyst. The invention has the advantages of low price of the adopted reagent, short production flow and better hydrogen evolution effect of the obtained catalyst as shown by electrochemical tests.

Description

Catalyst for hydrogen evolution by electrolyzing water and preparation method and application thereof

Technical Field

The invention belongs to the field of electrocatalysis, and particularly relates to carbon-nitrogen doped carbon (NC) base molybdenum carbide (Mo)₂C) Composite materials and methods for making the same.

Background

In the present society, energy crisis and environmental pollution have become more severe, threatening the survival and development of human beings. Hydrogen energy is a very important energy source, and due to its high energy density and environmentally friendly nature, it is considered to be an ideal energy carrier for sustainable energy storage and an alternative to fossil fuels. At present, the production of hydrogen depends on the fossil fuel industry, so that a plurality of problems are faced, such as low hydrogen purity and higher cost; the hydrogen and oxygen are generated by decomposing water by using current, so that the hydrogen production method is very effective, the production cost is relatively low, and the purity of the prepared hydrogen is high.

The hydrogen production reaction by electrolysis of water is considered to be an efficient way for large-scale industrial hydrogen production. Among them, noble metals exhibit extremely excellent catalytic activity, for example, Pt-based catalysts are currently recognized as hydrogen production catalysts for electrolysis with the best properties, but noble metals cannot be popularized and applied on a large scale because of limited reserves and high price. Molybdenum carbide is a highly efficient hydrogen evolution catalyst that is believed to replace Pt-based catalysts, and in order to increase conductivity and improve mass transfer, hydrogen evolution catalysts are often composited with various carbon supports to improve catalytic performance.

Disclosure of Invention

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

In order to achieve the purpose, the invention provides the following technical scheme:

the invention provides a preparation method of a hydrogen evolution catalyst for water electrolysis, which comprises the following steps:

the method comprises the following steps: carrying out oxidation treatment on the carbon carrier, washing and drying in a vacuum drying oven;

step two: dissolving the carbon carrier and ammonium molybdate treated in the step one in deionized water, adding a certain amount of aniline, stirring in an ice bath until the ammonium molybdate is dissolved, and keeping the temperature constant;

step three: preparing a certain concentration of over-sulfurAmmonium salt (NH)₄)₂S₂O₈Adding the HCl solution into the solution obtained in the second step, and continuously stirring;

step four: the mixed solution is changed into dark green, the lower layer sediment is centrifugally taken down and washed for a plurality of times, and a molybdenum-doped carbon-polyaniline precursor is obtained after drying in a vacuum drying oven;

step five: and grinding the precursor in the fourth step into powder, putting the powder into a tube furnace, carrying out heat treatment under a protective atmosphere and naturally cooling to obtain the carbon-nitrogen doped carbon-based molybdenum carbide material.

Based on the above technical solution, preferably, the carbon material in the step one is any one of graphite and carbon nanotubes. Graphene oxidation treatment, namely preparing graphene oxide from graphite by using a Hummers oxidation method. And the oxidation treatment of the carbon nano tube comprises the steps of refluxing the carbon nano tube in concentrated nitric acid at the temperature of 60-70 ℃ for 3-4 hours and washing the carbon nano tube to be neutral.

Based on the technical scheme, preferably, the drying in the first step and the drying in the fourth step is drying for 12-14 hours in a vacuum drying oven at the temperature of 60-80 ℃.

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

Based on the technical scheme, preferably, in the fifth step, the temperature is raised to 750-800 ℃ at a speed of 3-5 ℃/min for treatment for 3-4 h.

In another aspect of the present invention, there is provided a hydrogen evolution catalyst for electrolyzed water prepared by the above method, wherein the catalyst-supported catalyst has a carbon-nitrogen doped carbon composite carrier as a carrier and molybdenum carbide as a supported material. .

In still another aspect, the invention provides an application of the hydrogen evolution catalyst for water electrolysis, which is used for hydrogen evolution reaction of water electrolysis.

The invention has the advantages that:

1. according to the invention, the coordination of aniline and molybdate ions is utilized, and the aniline and molybdate ions are uniformly polymerized on the carbon carrier, so that the dispersion of molybdenum elements is facilitated, the agglomeration in the subsequent high-temperature process is avoided, more active sites are exposed, and the electrocatalytic activity is improved;

2. the preparation method has the advantages of simple preparation process, controllable operation, good catalytic performance and potential for industrial application.

Drawings

FIG. 1 shows Mo prepared in example 1₂X-ray diffraction patterns of C/rGO-NC;

FIG. 2 shows Mo prepared in example 3₂X-ray diffraction analysis chart of C/NC;

FIG. 3 shows Mo prepared in example 2₂X-ray diffraction analysis diagram of C/CNTs-NC;

FIG. 4 shows Mo prepared in example 1₂C/rGO-NC scanning electron microscope picture;

FIG. 5 shows Mo prepared in example 3₂C/NC scanning electron microscope picture;

FIG. 6 shows Mo prepared in example 2₂A scanning electron microscope image of C/CNTs-NC;

FIG. 7 shows Mo prepared in example 1₂EDX element distribution map of C/rGO-NC;

FIG. 8 shows Mo prepared in example 3₂EDX element distribution diagram of C/NC;

FIG. 9 shows Mo prepared in example 2₂EDX element distribution diagram of C/CNTs-NC;

FIG. 10 is the linear sweep voltammogram of examples 1, 2, and 3;

FIG. 11 is a Tafel slope chart for examples 1, 2, and 3.

Detailed Description

Example 1

Graphene Oxide (GO) was prepared using Hummers method: adding 1g of graphite flake and 1g of sodium nitrate into 50mL of concentrated sulfuric acid, stirring for 2h in an ice bath, slowly adding 4g of potassium permanganate powder, continuously stirring in the ice bath, transferring the mixture into a 35 ℃ oil bath, carrying out medium-temperature reaction for 2h, dropwise adding 150mL of deionized water, heating to 95 ℃, dispersing the product in the deionized water after the dropwise addition is finished, adding 10mL of hydrogen peroxide and 100mL of 10% wt hydrochloric acid, stirring and centrifuging, putting the precipitate into a dialysis bag, dialyzing with the deionized water until the precipitate does not contain sulfate ions, freezing the product with liquid nitrogen, and drying in a freeze dryer to obtain the graphene oxide. 30mg of graphene oxide and 60mg of ammonium molybdate are dissolved in 20mL of deionized waterIn water, 95mg of aniline is added dropwise and evenly dispersed in ice bath with stirring, 10mL of prepared 0.5MHCl solution containing 0.4g of ammonium persulfate is added dropwise, and the mixture reacts for 4 hours in ice bath. The solution turns into dark green, is centrifuged and washed by deionized water for a plurality of times, and is put into a vacuum drying oven for drying for 12 hours at the temperature of 60 ℃ to obtain the molybdenum-doped graphene oxide-polyaniline precursor. Putting the precursor into a porcelain boat, heating to 800 ℃ at a speed of 5 ℃/min in a tube furnace by taking nitrogen as protective gas and keeping for 3h, and naturally cooling to obtain Mo₂C/rGO-NC catalyst.

Example 2

Performing surface oxidation treatment on Carbon Nanotubes (CNTs): adding 1g of multi-walled carbon nano-tube into 30mL of concentrated nitric acid, stirring, refluxing for 3h under an oil bath at 60 ℃, filtering the product, washing the product with deionized water to be neutral, and drying the product for 12h at 60 ℃ in a vacuum drying oven to obtain the nano-tube. And (2) dissolving 30mg of surface oxidation carbon nano tube and 60mg of ammonium molybdate in 20mL of deionized water, dropwise adding 95mg of aniline, stirring and uniformly dispersing in an ice bath, dropwise adding 10mL of prepared 0.5MHCl solution containing 0.4g of ammonium persulfate, and reacting for 4 hours in the ice bath. The solution turns into dark green, is centrifuged and washed by deionized water for a plurality of times, and is put into a vacuum drying oven for drying for 12 hours at the temperature of 60 ℃ to obtain the molybdenum-doped carbon nano tube-polyaniline precursor. Putting the precursor into a porcelain boat, heating to 800 ℃ at a speed of 5 ℃/min in a tube furnace by taking nitrogen as protective gas and keeping for 3h, and naturally cooling to obtain Mo₂C/CNTs-NC catalyst.

Example 3

60mg of ammonium molybdate is dissolved in 20mL of deionized water, 95mg of aniline is added dropwise and uniformly stirred and dispersed in ice bath, 10mL of prepared 0.5MHCl solution containing 0.4g of ammonium persulfate is added dropwise, and the mixture reacts for 4 hours in the ice bath. The solution turns into dark green, is centrifuged and washed by deionized water for a plurality of times, and is put into a vacuum drying oven for drying for 12 hours at the temperature of 60 ℃ to obtain the molybdenum-doped polyaniline precursor. Putting the precursor into a porcelain boat, heating to 800 ℃ at a speed of 5 ℃/min in a tube furnace by taking nitrogen as protective gas and keeping for 3h, and naturally cooling to obtain Mo₂C/NC catalyst. Example 3 the same procedure as in example 1 and example 2 was followed, except that no carbon support was added.

As can be seen from FIGS. 1, 2 and 3, the diffraction peaks of the catalyst are less pronounced, indicating molybdenum carbideThe catalyst has lower crystallinity, is beneficial to exposing more active sites, can show characteristic peaks of molybdenum carbide at 38.0 degrees, 39.6 degrees, 52.3 degrees, 61.9 degrees and 69.8 degrees, and are respectively classified as hexagonal β -Mo₂The (002), (101), (102), (110) and (103) crystal planes of C (JCPDS 65-8766). The above results demonstrate that the production process of the present invention is advantageous in forming more oxygen vacancies.

As can be seen from fig. 4, the catalyst basically maintains the original morphology of the carbon-supported graphene oxide, and has a two-dimensional sheet structure with many pores, which is beneficial to the transport of substances.

As can be seen from fig. 5, the particle size of the molybdenum carbide catalyst synthesized by using polyaniline as a precursor is smaller, which is beneficial to exposing more active sites.

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

Electrocatalytic testing: 5mg of the catalyst and 80. mu.L of 5% Nafion solution were dispersed in an isopropanol solution and sonicated for 30min to give a catalyst slurry. 10 mu L of catalyst slurry is moved on a glassy carbon electrode with the diameter of 5mm and dried into a thin film catalyst layer under an infrared baking lamp. In a three-electrode system (glassy carbon electrode is a working electrode, a carbon rod is a counter electrode, a calomel electrode is a reference electrode, and a 0.5M sulfuric acid solution is an electrolyte solution), a linear sweep voltammetry curve is measured, and the test result is shown in figure 10 and is at 10mAcm^-2The catalyst was tested for overpotential. From the linear sweep voltammogram, a tafel plot was obtained for each sample, as shown in fig. 11. The test results are given in the following table:

test specimen	Overpotential (10 mAcm)^-2)	Tafel slope
			Examples1	55mV	109mV/dec
Example 2	27mV	115mV/dec
			Example 3	91mV	108mV/dec

The results show that the molybdenum carbide in the catalyst prepared by the preparation method has small particle size and low crystallinity, is beneficial to forming more oxygen vacancies and is beneficial to reaction; catalyst Mo prepared by adding carbon nano tube and graphene oxide as carbon source carrier₂C/CNTs-NC and catalyst Mo₂The C/rGO-NC has more excellent catalytic hydrogen evolution performance and lower overpotential.

Claims

1. A method for preparing a hydrogen evolution catalyst for electrolysis of water, characterized in that the method comprises the following steps:

the method comprises the following steps: oxidizing the carbon material, washing and vacuum drying;

step two: dissolving the carbon material treated in the step one and ammonium molybdate in deionized water, adding a certain amount of aniline, stirring in an ice bath until the ammonium molybdate is dissolved, and keeping the temperature constant;

step three: preparing a 0.5MHCl solution of 30-40 g/L ammonium persulfate, and adding the solution into the solution obtained in the second step, and continuously stirring for 4-6 hours to obtain a mixed solution;

step four: centrifugally washing and vacuum drying the mixed solution obtained in the step three to obtain a molybdenum-doped carbon-polyaniline precursor;

step five: and grinding the molybdenum-doped carbon-polyaniline precursor into powder, carrying out heat treatment in a protective atmosphere, and naturally cooling to obtain the catalyst.

2. The method for producing a hydrogen evolution catalyst for electrolyzed water according to claim 1, wherein the carbon material is graphite, and the oxidation treatment is a Hummers oxidation method for producing graphene oxide from graphite; the carbon material is carbon nano tube, and the oxidation treatment is to reflux and wash the carbon nano tube in concentrated nitric acid at 60 ℃ to be neutral.

3. The method for preparing a hydrogen evolution catalyst for electrolyzed water according to claim 1, wherein the vacuum drying in the first step and the fourth step is drying in a vacuum drying oven at 60-80 ℃ for 12-14 h.

4. The method of claim 3, wherein the protective gas in step five is any one of nitrogen and argon.

5. The method for preparing a hydrogen evolution catalyst for electrolyzed water according to claim 3, wherein the heat treatment in the fifth step is a treatment of raising the temperature to 750-800 ℃ at a rate of 3-5 ℃/min for 3-4 hours.

6. A hydrogen evolution catalyst for electrolyzed water prepared by the method of any one of claims 1 to 5, characterized in that the catalyst is a supported catalyst, the carrier is a carbon-nitrogen doped carbon composite carrier, and the supported object is molybdenum carbide.

7. Use of the hydrogen evolution catalyst for the electrolysis of water according to claim 6, characterized in that the catalyst is used in the hydrogen evolution reaction of electrolysis water.