CN113134374A

CN113134374A - MoO2-Mo2C hydrogen evolution catalytic material and preparation method and application thereof

Info

Publication number: CN113134374A
Application number: CN202110444361.5A
Authority: CN
Inventors: 张睿智; 罗泽; 王子野; 肖新宇
Original assignee: Hunan Institute of Technology
Current assignee: Hunan Institute of Technology
Priority date: 2021-04-23
Filing date: 2021-04-23
Publication date: 2021-07-20
Anticipated expiration: 2041-04-23
Also published as: CN113134374B

Abstract

MoO ₂ -Mo ₂ C hydrogen evolution catalytic material, preparation method and application thereof, relate to the technical field of electrocatalytic materials, the method for preparing MoO ₂ -Mo ₂ C hydrogen evolution catalytic material of the present invention is simple, low in cost, and the prepared product has a large specific surface area, There are many active sites that can be contacted. Due to the unique heterostructure of the MoO ₂ ‑Mo ₂ C composite material, it has higher catalytic activity, faster catalytic rate and catalytic performance than the existing molybdenum-based hydrogen evolution catalysts. stability. After testing, the above-mentioned MoO ₂ -Mo ₂ C composite material has relatively ideal overpotential and Tafel slope as a cathode catalyst, and the performance degradation after 1000 cycles is only 2.5%. In addition, Mo resources are relatively abundant and the cost of raw materials is low. The above-mentioned MoO ₂ ‑Mo ₂ C hydrogen evolution catalytic materials exhibit the possibility of replacing Pt.

Description

MoO2-Mo2C hydrogen evolution catalytic material and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrocatalytic materialsIn particular to a MoO₂-Mo₂C hydrogen evolution catalytic material, preparation method and application thereof.

Background

The hydrogen fuel cell has higher theoretical energy density and is a promising fuel cell for replacing an automobile internal combustion engine. The difficulties of popularization and application of the hydrogen fuel cell are as follows: hydrogen production, storage and efficient utilization of hydrogen. The hydrogen production technology is the problem to be solved firstly, and water electrolysis is the most common hydrogen production means at present. When water is electrolyzed, the anode generates oxygen evolution reaction and the cathode generates hydrogen evolution reaction. The essence of electrocatalysis is to reduce the overpotential of the two half-reactions by using a catalyst, thereby reducing the energy consumption of the water electrolysis process. Suitable electrocatalysts are particularly important in the process of producing hydrogen by electrolyzing water.

Platinum is the most well-known hydrogen evolution catalyst at present, and the overpotential of Pt is almost negligible. But the scarcity and high cost of platinum limits its widespread use. In recent years, hydrogen evolution catalysts for transition metal Mo have been increasingly studied. Chinese patent document CN105797758A discloses graphene-loaded MoO used for electrocatalytic hydrogen evolution₂-Mo₂Method for synthesizing catalyst C, which adopts ammonium molybdate, aniline and hydrochloric acid to synthesize MoO₂-Mo₂C precursor, mixing and grinding Graphene Oxide (GO) and the precursor, and calcining to obtain graphene-loaded MoO₂-Mo₂And C, material. The electrochemical hydrogen production test result of the material shows that the catalytic effect is good, but still needs to be improved. In addition, the GO needs to be calcined at the temperature of 750 ℃ after being mixed with the precursor, and the excessive reaction temperature is not beneficial to saving energy consumption.

Disclosure of Invention

One of the objects of the present invention is to provide a method for preparing MoO₂-Mo₂C hydrogen evolution catalytic material, the reaction temperature adopted by the method is lower and the prepared MoO can be enabled to be₂-Mo₂The C heterostructure material has higher catalytic activity.

To achieve the above object, MoO in the present invention₂-Mo₂The preparation method of the C hydrogen evolution catalytic material comprises the following steps:

1）H_xMoO₃synthesis of a precursor: taking a proper amount of MoO₃Adding into mixed solution of ethylene glycol and anhydrous ethanol, and stirring to obtain MoO₃Uniformly dispersing the mixture in a mixed solution to form a suspension, placing the suspension in a reaction kettle for hydrothermal reaction at the temperature of about 190-210 ℃ to obtain a tan product, cleaning and drying the tan product to obtain black H_xMoO₃a/C precursor;

2) synthesis of MoO2-Mo2C nano-microspheres: h obtained in the step 1)_xPerforming heat treatment on the MoO3/C precursor under the protection of pure argon atmosphere, wherein the heat treatment temperature is about 640-660 ℃, the heating rate is about 4-6 ℃/min, the argon flow is about 290-310 sccm, cooling to room temperature after the reaction is finished to obtain a brown powder product, then introducing a mixed gas of oxygen and argon to passivate the product, and changing the color of the powder from brown to brownish purple after the passivation to obtain the MoO-modified MoO-C precursor₂-Mo₂MoO composed of C nano-microspheres₂-Mo₂C hydrogen evolution catalytic material.

Wherein, in the step 2), the oxygen content in the mixed gas is about 9% to about 11%.

Wherein, in the step 1), the volume ratio of the glycol to the absolute ethyl alcohol in the mixed solution is about 1: 1.

wherein, in step 1), the MoO₃The ratio of the solution to the mixed solution is 0.1g of MoO₃Approximately corresponding to 15ml of the mixed solution.

Wherein, in step 2), the heat treatment time is about 4h to about 6 h.

In addition, the invention also relates to a MoO₂-Mo₂A C hydrogen evolution catalytic material consisting of solid microspheres with a diameter of about 0.9 to about 1.1 [ mu ] m, the solid microspheres comprising a main component of MoO₂And the main component of the core is MoO coated outside the core₂Mo formed by carbonization₂C, surface layer.

Wherein, the MoO is₂-Mo₂The C hydrogen evolution catalytic material is prepared by the preparation method.

In addition, the invention also relates to the MoO₂-Mo₂The application of the C hydrogen evolution catalytic material in the cathode electrode of the water electrolysis, the anode of the hydrogen fuel cell and the hydrogen evolution reaction catalyst in the hydrogen production method by water electrolysis.

Preparation of MoO by the invention₂-Mo₂The method for preparing the C hydrogen evolution catalytic material is simple and has low cost (the synthetic raw material is relatively cheap MoO₃Ethylene glycol and absolute ethyl alcohol) prepared by the method, the specific surface area of the prepared product is large, and the number of active sites which can be contacted is large due to MoO₂-Mo₂The C composite material has a unique heterostructure, so that the C composite material has higher catalytic activity, higher catalytic rate and higher catalytic stability than the existing molybdenum-based hydrogen evolution catalyst. After testing, the MoO is prepared₂-Mo₂The C composite material as a cathode catalyst has ideal overpotential and Tafel slope, the performance attenuation after 1000 cycles is only 2.5%, and the MoO has rich Mo resource, low cost₂-Mo₂The C hydrogen evolution catalytic material exhibits the possibility of replacing Pt, which will greatly reduce the cost of water electrolysis. In addition, the invention carries out heat treatment at 650 ℃, compared with the prior art document (the calcining temperature is 750 ℃), the heat treatment temperature of the invention is lower, and the lower reaction temperature is beneficial to saving energy consumption.

Description of the drawings:

FIG. 1 is MoO₂、Mo₂C and MoO₂-Mo₂XRD diffraction pattern of C heterostructure;

in FIG. 2, (a) and (b) are precursors H_xMoO₃Low and high power SEM pictures of/C;

in FIG. 3, (a) and (b) are MoO, respectively₂-Mo₂Low power and high power SEM pictures of C heterostructure;

in FIG. 4, (a) is MoO₂-Mo₂C transmission electron imaging graph of heterostructure, and (b) MoO₂-Mo₂A C heterostructure conversion layer HRTEM image;

FIG. 5 shows Mo₂C、MoO₂-Mo₂C、MoO₂Hydrogen evolution electrochemical linear voltammetry scan curves with 20% Pt/C;

FIG. 6 shows MoO₂-Mo₂Tafel plot of C versus 20% Pt/C;

FIG. 7 shows MoO₂-Mo₂C LSV curves at 1 st and 1000 th circles in cyclic voltammetry.

Detailed Description

For the understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention. It should be noted that the following examples are carried out in the laboratory, and it should be understood by those skilled in the art that the amounts of the components given in the examples are merely representative of the proportioning relationship between the components, and are not specifically limited.

One, H_xMoO₃And synthesizing a/C precursor.

First, 0.2g of commercial MoO was accurately weighed with an electronic balance (AEL-200)₃Placing the medicine in a mixed solution of about 15ml ethylene glycol and about 15ml anhydrous ethanol, and stirring for about 6h to mix the mixed solution with MoO₃Mixing the medicines, placing the suspension into a 50ml inner liner of a reaction kettle, performing hydrothermal reaction at about 200 deg.C (about 190-210 deg.C) for about 6 hr to obtain brown product, centrifuging the product with ethanol and water for several times, drying in a drying oven at about 80 deg.C for about 12 hr, and drying to obtain black H_xMoO₃and/C precursor. Commercial MoO₃Has a layered structure, and non-metal cations can be inserted into van der Waals gaps to form a molybdenum-based precursor H_xMoO₃and/C. For hydrogenated MoO₃The charge transfer from H to O changes the H atom to a proton and causes partial reduction of the adjacent Mo atom, so that a weaker but more reactive Mo-O bond is formed by the free insertion of the H atom into the MoO₃The heterogeneous catalytic reaction in (2) gives a large amount of H_xMoO₃the/C precursor and the H source are provided by ethylene glycol and ethanol which participate in the reaction.

Secondly, synthesizing a target product.

Subjecting the precursor H obtained above to_xMoO3/C was heat treated in a tube furnace at about 650 deg.C (about 640-660 deg.C) for about 5h (about 4-6 h, as the case may be) in pure argon atmosphere, at a temperature rise rate of about 5 deg.C/min (about 4-6 deg.C/min), and at an argon flow rate of about 300sccm (about 290-310 sccm for standard cubic centimeters per minute, considering control errors and other objective reasons). After the reaction is finished and the temperature is cooled to room temperature, introducing mixed gas of oxygen and argon (O in the mixed gas) into the tubular furnace₂About 10%, for example about 9% -11%) for about 2 h. It should be noted that the above step of introducing the mixed gas after cooling to room temperature is very important, in relation to the hydrogen evolution catalytic activity of the sample. The mixed gas is introduced to passivate the sample and enable the treated sample to have higher catalytic activity. And (4) changing the color of the powder from brown to brownish purple after passivation to obtain the required target product.

In general, the synthesis of the target product comprises two parts, the first step is hydrothermal synthesis of H_xMoO₃and/C precursor. And secondly, performing heat treatment on the precursor in an argon-protected tube furnace (OTF-1200X, crystal of fertilizer combining department), cooling to room temperature, and introducing mixed gas of oxygen and argon to perform passivation treatment on the product so as to improve the catalytic activity of the product.

The preparation process has simple process and low cost (the synthetic raw material is cheap MoO₃Ethylene glycol and absolute ethyl alcohol) and the temperature of the heat treatment process is lower, and the lower reaction temperature is beneficial to saving energy consumption.

And thirdly, characterizing the product.

The product obtained in step two and the highly crystalline MoO used as a comparative analysis are shown in FIG. 1₂And Mo₂XRD profile of C. Highly crystalline MoO₂The XRD of (PDF # 86-0135) can be compared, and the diffraction peaks of 26.004 degrees, 36.948 degrees and 49.899 degrees are respectively corresponding to (011), (-211) and (-312) diffraction planes which can be clearly observed in the figure. Mo₂XRD contrast of C (PDF # 00-03)5-0787），Mo₂The characteristic peaks of C are located at 34.354 DEG, 39.392 DEG and 61.527 DEG, which correspond to the (100), (101) and (110) crystal planes, respectively, and the main peak at 39.392 DEG, which corresponds to the (101) plane, is high and sharp. MoO is visible from the XRD pattern of the product₂And Mo₂The diffraction peaks of C, (-111) and (-211) strong peaks indicate that the product is made of MoO₂And Mo₂C is compounded. Compared with Mo₂The main peak of C, corresponding to the (101) crystal face, has obvious degradation, which indicates that the main body of the product is MoO₂In the outer layer, part of Mo is stacked₂C, which is to lead to Mo₂The main peak of C is degraded.

For synthetic H_xMoO₃And performing scanning electron microscope analysis on the/C precursor and a product prepared by subsequent heat treatment. It can be observed from FIG. 2 that the surface is relatively smooth H_xMoO₃the/C diameter is 1.2-1.4 mu m. As can be seen from FIG. 3, the MoO obtained after the heat treatment₂-Mo₂The C composite material still keeps micro-sphere shape microscopically and MoO₂-Mo₂The average diameter of the C heterostructure is reduced to 0.9-1.1 μm. MoO by transmission electron microscope₂-Mo₂C heterostructure study, as shown in fig. 4 (a), it can be observed that the nanoparticles are the main building blocks of the solid microspheres, and these nano-scale building blocks can provide a large number of active sites for the hydrogen evolution catalytic process. MoO₂-Mo₂HRTEM image of C-heterostructure transition layer is shown in FIG. 4 (b), with lattice spacings in the outer stripes of 0.2278nm and 0.2419nm, and Mo₂C (101) plane and MoO₂(211) The monoclinic plane matches the fit, indicating an external transition from oxide to carbide. This also means that the carbon derived component acts as a "buffer" to limit grain growth and then acts as a "glue" to build up the MoO₂-Mo₂C heterosecondary structure, this unique microstructure and Mo involved in electrical conduction₂The C phase is favorable for ion diffusion and has good electronic conductivity and structural stability.

And fourthly, testing the performance.

Weighing 3-5mg MoO by using an electronic balance₂-Mo₂Sample CThe sample was mixed with 200. mu.L of ethanol and 800. mu.L of deionized water in a microcentrifuge tube. The mixed suspension was then inserted into a prepared foam pad and 80. mu.L of Nafion (Sigma Aldrich) was added to the microcentrifuge tube. The foam pad was placed in an ultrasonic cleaner (KQ 2200, ultrasonic instruments, Kunshan) for 30min, and 5. mu.L of the suspension was applied by a pipette onto a glassy carbon electrode having an active area of 3mm in diameter. And finally, covering the glassy carbon electrode by using a beaker, and placing the glassy carbon electrode in an incubator at 80 ℃ for drying for 6 hours, thereby completing the preparation of the working electrode. The test method comprises the following steps: the hydrogen evolution electrochemical performance tests were all performed on an electrochemical workstation (CHI 660E, shanghai chen hua). A three-electrode test system is used for testing the catalytic performance of the catalyst, a saturated calomel electrode is used as a reference electrode, a graphite rod with the diameter of 6mm is used as a counter electrode, and 0.5M sulfuric acid is used as electrolyte. X-ray diffraction (XRD) analysis was performed using a Rigaku D/max2500, Cu-K α radiation diffractometer and scanning electron microscopy was performed using a FEI Nova NanoSEM 230.

Before the linear voltammetric sweep test, 10 cycles of cyclic voltammetric sweep were first performed to activate the electrode-forming active material at a sweep rate of 50mv/s in order to obtain a stable polarization curve. The sweep range of the linear voltammetry test is-0.5-0.1V (vs RHE), and the sweep rate is 2 mv/s. The test environment temperature was 25 ℃, and all test voltage results were measured relative to the Reversible Hydrogen Electrode (RHE). The cycle stability was tested by comparing the LSV curve of the catalyst after 1000 scans with the first LSV curve.

The voltage with respect to the hydrogen electrode is converted by nernst formula (1):

E(vs RHE)=E(vs SCE)+0.242+0.059×pH (1) ；

the Tafel Slope (Tafel Slope) is converted into (2):

η=a+b lg(-j) (2)；

HER catalytic performance test:

for the prepared sample MoO₂-Mo₂C and commercial 20% Pt/C at 0.5M H₂SO₄Linear Sweep Voltammetry (Linear Sweep Voltammetry) electrochemical performance test is carried out in electrolyte to research hydrogen evolution catalytic activity of the electrochemical performance testTwo polarization curves were obtained, as shown in FIG. 5, from which the MoO was seen₂-Mo₂The initial voltages for C and 20% Pt/C were 68mV and 21mV, respectively. At 10mA cm^-2At current density of (3), MoO₂-Mo₂The overpotentials for C and 20% Pt/C were 161mV and 15mV, respectively.

FIG. 6 shows MoO₂-Mo₂Tafel slope curve of C versus 20% Pt/C, shown in FIG. 6, MoO₂-Mo₂The Tafel slopes of C and 20% Pt/C were 69mV dec^-1、42mV dec^-1. From b =2.3RT/α F, MoO can be known₂-Mo₂C follows the Volmer-Heyrovsky reaction mechanism during electrocatalysis due to the reaction at 0.5M H₂SO₄In acidic electrolyte, MoO₂-Mo₂The heterostructure of C improves the electronic conductivity and provides a wider diffusion channel for hydrogen ions. Passing chronopotentiometric test at 0.5M H₂SO₄In the electrolyte, after circulating for 1000 circles, MoO₂-Mo₂The LSV curve of C is shown in FIG. 7, MoO₂-Mo₂The potential decay of C was 2.5%, indicating that MoO₂-Mo₂C has good hydrogen evolution electrocatalysis cycle performance.

From the above analysis results, it can be seen that the MoO having the hydrogen evolution catalytic effect was prepared in the above examples₂-Mo₂The C composite material can be seen from the preparation process, the process method is simple, and the cost is low (the synthetic raw material is relatively cheap MoO₃Ethylene glycol and absolute ethyl alcohol) and the prepared product has a unique heterostructure, a large specific surface area and many active sites which can be contacted, due to the MoO₂-Mo₂The C composite material has a unique heterostructure, so that the C composite material has higher catalytic activity, higher catalytic rate and higher catalytic stability than the existing molybdenum-based hydrogen evolution catalyst. According to the test result, the MoO can be determined₂-Mo₂The C composite material as a cathode catalyst has ideal overpotential and Tafel slope, and the performance attenuation after 1000 cycles is only 2.5%, although the catalytic performance of the C composite material is different from that of Pt, Mo resources are relatively rich, the raw material cost is low,the possibility of replacing Pt is still exhibited, and thus, it will be possible to greatly reduce the cost of electrolytic water. In addition, it will be appreciated by those skilled in the art that MoO based on the foregoing is₂-Mo₂The electrochemical performance of the C composite material also has potential value in the application of the anode of the hydrogen fuel cell.

The above embodiments are preferred implementations of the present invention, and the present invention can be implemented in other ways without departing from the spirit of the present invention.

Finally, it should be emphasized that some of the descriptions of the present invention have been simplified to facilitate the understanding of the improvements of the present invention over the prior art by those of ordinary skill in the art, and that other elements have been omitted from this document for the sake of clarity, and those skilled in the art will recognize that these omitted elements may also constitute the content of the present invention.

Claims

1. the preparation method of MoO ₂ -Mo ₂ C hydrogen evolution catalytic material, is characterized in that, comprises the following steps:

1) Synthesis of H _x MoO3/C precursor: Take an appropriate amount _of MoO3 and add it to the mixed solution of ethylene glycol and absolute ethanol, stir well to make _MoO3 evenly dispersed in the mixed solution to form a suspension, and place the suspension in the mixed solution. A hydrothermal reaction is carried out in the reaction kettle, and the temperature of the hydrothermal reaction is about 190°C to about 210°C, and the reaction obtains a tan product, and the tan product is washed and dried to obtain a black H _x MoO ₃ /C precursor;

2) Synthesis of MoO2-Mo2C nano-microspheres: heat treatment of the H _x MoO3/C precursor obtained in step 1) under the protection of pure argon atmosphere, the heat treatment temperature is about 640°C to about 660°C, and the heating rate is about 4°C/min - About 6°C/min, the argon flow rate is about 290sccm-about 310sccm, after the reaction is completed, it is cooled to room temperature to obtain a brown powder product, and then the mixed gas of oxygen and argon is introduced to passivate the product. After passivation, the powder color changes from The brown color turns to brownish purple, and the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material composed of MoO ₂ -Mo ₂ C nano-microspheres is obtained.

2 . The preparation method of the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material according to claim 1 , wherein: in step 2), the oxygen content in the mixed gas is about 9% to about 11%. 3 .

3. The preparation method of MoO ₂ -Mo ₂ C hydrogen evolution catalytic material according to claim 1 or 2, characterized in that: in step 1), the volume ratio of ethylene glycol and absolute ethanol in the mixed solution is about 1: 1.

4. The preparation method of the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material according to claim 1 or 2, wherein in step 1), the ratio of the MoO ₃ to the mixed solution is approximately corresponding to every 0.1 g MoO ₃ 15ml mixed solution.

5 . The preparation method of the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material according to claim 1 or 2, characterized in that: in step 2), the heat treatment time is about 4 h to about 6 h.

6. MoO ₂ -Mo ₂ C hydrogen evolution catalytic material, characterized in that: it is composed of solid microspheres with a diameter of about 0.9µm-about 1.1µm, and the solid microspheres comprise an inner core whose main component is MoO ₂ and is coated on the outside of the inner core And the main component is the surface layer of Mo ₂ C formed by the carbonization of MoO ₂ .

7 . The MoO ₂ -Mo ₂ C hydrogen evolution catalytic material according to claim 6 is characterized in that: it is prepared by the preparation method described in any one of claims 1-5. 8 .

8. The application of the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material described in claim 6 or 7 in the water electrolysis negative electrode.

9. The application of the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material described in claim 6 or 7 as a hydrogen evolution reaction catalyst in a method for producing hydrogen by electrolysis of water.

10 . The application of the MoO ₂ -Mo ₂ C hydrogen evolution catalytic material according to claim 6 or 7 in a positive electrode of a hydrogen fuel cell. 11 .