CN110359061B

CN110359061B - Preparation method of molybdenum dioxide nanowire/nanosheet thin film array with good electrocatalytic hydrogen evolution performance

Info

Publication number: CN110359061B
Application number: CN201910713671.5A
Authority: CN
Inventors: 张勇; 刘志民; 魏浩山; 崔接武; 王岩; 秦永强; 舒霞; 吴玉程
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2019-08-02
Filing date: 2019-08-02
Publication date: 2021-04-13
Anticipated expiration: 2039-08-02
Also published as: CN110359061A

Abstract

The invention discloses a preparation method of a molybdenum dioxide nanowire/nanosheet thin film array with good electrocatalytic hydrogen evolution performance, which comprises the following steps: weighing 0.6-0.8g of ammonium molybdate in a beaker, adding 0.2-0.3mL of 30% hydrogen peroxide and 0.1-0.3mL of absolute ethyl alcohol, adding deionized water to 30mL, stirring until the solution is completely dissolved, then placing the solution in a polytetrafluoroethylene inner container, placing a 2-4cm molybdenum net in the polytetrafluoroethylene inner container, placing the polytetrafluoroethylene inner container in a metal reaction kettle and screwing up, placing the polytetrafluoroethylene inner container in a hydrothermal oven for hydrothermal reaction at the temperature of 150 plus materials and 230 ℃ for heat preservation for 6-15h, finally repeatedly washing a sample by deionized water for several times, and preserving the heat at the temperature of 60 ℃ for 1h and drying to obtain the molybdenum dioxide nanowire/nanosheet film array with black ink appearance. The product synthesized by the method has larger comparative area and more active sites, and overcomes the defect of poor oxidative conductivity.

Description

Preparation method of molybdenum dioxide nanowire/nanosheet thin film array with good electrocatalytic hydrogen evolution performance

Technical Field

The invention relates to a preparation method of a molybdenum dioxide nanowire/nanosheet thin film array with good electrocatalytic hydrogen evolution performance, and different hydrogen evolution characteristics generated by different morphological characteristics of the molybdenum dioxide nanowire/nanosheet thin film array are analyzed at the same time.

Background

At present, energy is more and more tense, green energy is urgently sought, hydrogen production by water electrolysis is an efficient pollution-free hydrogen production mode, at present, Pt/C electrode materials are more used, but Pt is limited in application due to high price and rare content. Molybdenum dioxide materials suffer from poor resistance and hydrogen evolution. The test method adopted by the invention is different from the traditional test method. The hydrogen evolution characteristic of the semiconductor catalytic material is analyzed by an electrochemical method, the hydrogen evolution capacity of the semiconductor material is analyzed through the overpotential, the starting point position and the Tafel slope, and the current of the semiconductor material can be influenced by an electric field, an interface, the atmosphere of the interface and various other factors of the semiconductor material per se to actually produce hydrogen. The gas chromatography and the relation between the specific numerical value of hydrogen production and the current and the potential thereof are measured under high vacuum degree.

Disclosure of Invention

The invention aims to provide a preparation method for growing molybdenum oxide nanowires and nanosheets on a molybdenum mesh substrate, and a nanowire and nanosheet film array with a (001) crystal face is prepared by a simple one-step hydrothermal method. The main problem to be solved is to improve the problem of poor resistance and hydrogen evolution of the existing molybdenum dioxide material.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of a molybdenum dioxide nanowire/nanosheet thin film array with good electrocatalytic hydrogen evolution performance comprises the following steps:

weighing 0.6-0.8g of ammonium molybdate in a beaker by adopting a traditional hydrothermal synthesis process, adding 0.2-0.3mL of 30% hydrogen peroxide and 0.1-0.3mL of absolute ethyl alcohol, adding deionized water to 30mL, stirring until the ammonium molybdate is completely dissolved, then placing the solution in a polytetrafluoroethylene inner container, placing a 2-4cm molybdenum net in the polytetrafluoroethylene inner container, placing the polytetrafluoroethylene inner container in a metal reaction kettle and screwing down, placing the polytetrafluoroethylene inner container in a hydrothermal oven for hydrothermal reaction at the temperature of 150-.

Preferably, the concentration of the precursor ammonium molybdate is 0.01618-0.02158M/L.

Preferably, the concentration of the hydrogen peroxide in the step 1 is 0.06526-0.09790M/L

Preferably, the hydrothermal temperature of the hydrothermal reaction is 170-210 ℃, and the reaction time is 8-12 h.

Compared with the prior art, the invention has the beneficial effects that:

the method adopts the traditional hydrothermal synthesis process, adopts ammonium molybdate tetrahydrate as a precursor, and adopts trace hydrogen peroxide and ethanol thereof as a morphology control agent. The sizes of the nano wires and the nano sheets on the surface of the molybdenum net are controllable, and meanwhile, the molybdenum net substrate cannot be dissolved in low-concentration hydrogen oxide, so that the molybdenum net fibers and the molybdenum dioxide film have good synergistic effect. Meanwhile, the positively charged ammonium ions in the ammonium molybdate can ensure that the molybdenum dioxide directionally grows on the interface of the molybdenum net. The molybdenum net is used as a substrate and a molybdenum source, a pure-phase molybdenum dioxide product with a three-dimensional space structure can be obtained through the reaction with low-concentration hydrogen peroxide and the synergistic growth effect of ammonium molybdate, and meanwhile, post-treatment such as annealing and the like is not needed, so that the generation of molybdenum trioxide impurity phases is avoided. Ethanol with a certain concentration is selected as a stabilizer to react with hydrogen peroxide serving as an oxidant, so that molybdenum dioxide can selectively grow into a nano-sheet or nano-wire structure, meanwhile, the selective use of the ethanol ensures that the nano-sheet and the nano-wire are firmly combined with a molybdenum substrate, and other alcohols cannot achieve the effect. The obtained molybdenum dioxide nanowires and nanosheets have good electrolytic water hydrogen evolution characteristics. The method has the advantages of convenient operation, simple process and low cost, is easy to enlarge the manufacturing scale, and is very beneficial to large-scale production. The product synthesized by the method has smaller appearance, larger comparative area and more active sites, and overcomes the defect of poor oxidative conductivity. The electrochemical active area, the current density and the hydrogen evolution performance are improved. The invention utilizes Pofely gas phase detection system, photoelectrocatalysis reactor and electrochemical workstation. And introducing proper voltage parameters, observing current values and hydrogen evolution quantities corresponding to all the potentials, and analyzing the electron conversion efficiency and the hydrogen evolution efficiency.

Drawings

Fig. 1 is a scanning electron microscope image of the molybdenum dioxide nanowire thin film prepared in example 1 of the present invention.

FIG. 2 is an X-ray diffraction pattern of a molybdenum dioxide nanowire film prepared in example 1 of the present invention.

Fig. 3 is a scanning electron microscope image of the molybdenum dioxide nanosheet film prepared in example 2 of the present invention.

Figure 4 is an X-ray diffraction pattern of a molybdenum dioxide nanosheet film prepared in example 2 of the present invention.

Fig. 5 is a line graph of the relationship between the applied bias voltage and the hydrogen evolution amount of the molybdenum dioxide nanowires and nanosheets prepared in example 3 of the present invention.

Detailed Description

Example 1: the molybdenum dioxide nanowire film is prepared by taking hydrogen peroxide as a morphology control agent, and the traditional hydrothermal synthesis process is adopted, and ammonium molybdate tetrahydrate and 30% hydrogen peroxide are synthesized under the hydrothermal condition of 170-210 ℃.

The method comprises the following specific steps:

weighing 0.6-0.8g of ammonium molybdate in a beaker, adding 0.2-0.3mL of 30% hydrogen peroxide, adding deionized water to 30mL, stirring until the ammonium molybdate is completely dissolved, then placing the solution in a polytetrafluoroethylene inner container, placing a 2-4cm molybdenum net in the polytetrafluoroethylene inner container, placing the polytetrafluoroethylene inner container in a metal reaction kettle and screwing down, placing the polytetrafluoroethylene inner container in a hydrothermal drying oven, preserving heat for 8-12h at the temperature of 170 plus materials and 210 ℃, finally repeatedly washing a sample with deionized water for several times, preserving heat for 1h at the temperature of 60 ℃, and drying to obtain the molybdenum dioxide nanowire film array with black ink appearance.

FIG. 1 is a scanning electron microscope image of the molybdenum dioxide nanowire thin film prepared in example 1, wherein the image shows that the sample is a nanowire with a diameter of 10-50nm and a length of 100-200 nm.

FIG. 2 is an X-ray diffraction pattern of the molybdenum dioxide nanowire film prepared in example 1, and three very sharp peaks, which represent (100), (200) and (211) crystal planes corresponding to Mo, respectively. No other impurity peak, namely the pure-phase molybdenum dioxide film.

Example 2 was carried out: preparing a molybdenum dioxide nanosheet film by using the synergistic effect of hydrogen peroxide and ethanol:

ammonium molybdate tetrahydrate, 30 percent hydrogen peroxide and absolute ethyl alcohol are adopted for hydrothermal synthesis at the high temperature and the high pressure of 170-210 ℃.

The method comprises the following specific steps:

weighing 0.6-0.8g of ammonium molybdate in a beaker, adding 0.2-0.3mL of 30% hydrogen peroxide and 0.2-0.3mL of absolute ethyl alcohol, adding deionized water to 30mL, stirring until the solution is completely dissolved, then placing the solution in a polytetrafluoroethylene inner container, placing a 2-4cm molybdenum net in the polytetrafluoroethylene inner container, placing the polytetrafluoroethylene inner container in a metal reaction kettle and screwing up, placing the polytetrafluoroethylene inner container in a hydrothermal oven, preserving heat for 8-12h at the temperature of 170 plus materials and 210 ℃, finally repeatedly washing a sample by using deionized water for several times, preserving heat for 1h at the temperature of 60 ℃, and drying to obtain the black-appearing nanosheet molybdenum dioxide film array.

Fig. 3 is a scanning electron microscope image of the molybdenum dioxide nanosheet film prepared in example 2 of the present invention. The diffraction peak shown in FIG. 3 reflects that the sample is composed of orthorhombic nanoplatelets, with a width of 200-300nm and a thickness of 20-30 nm.

Figure 4 is an X-ray diffraction pattern of a molybdenum dioxide nanosheet film prepared in example 2 of the present invention, the peaks appearing as orthorhombic phase of molybdenum dioxide.

Example 3: analysis of electrocatalytic hydrogen evolution Performance

The Pofely reaction system device, the electrochemical workstation, the gas chromatography and condenser, and the vacuum pump are used for testing the hydrogen evolution amount. Specifically, the relationship between the hydrogen production amount and the voltage and current and the electron conversion efficiency thereof were measured. Taking a 4-2cm molybdenum net attached with nanowires and nanosheets as a working electrode, a pt sheet as a counter electrode and Ag/Agcl as a reference electrode, and placing the counter electrode and the Ag/Agcl into a three-electrode reactor containing 70ml of 0.5M dilute sulfuric acid. After the electrochemical workstation and the reactor are connected through vacuumizing, appropriate voltage parameters are introduced, the current values and the hydrogen evolution quantity corresponding to all the potentials are detected as shown in figure 5, and the hydrogen evolution efficiency of the nanowire is obviously superior to that of the nanosheet.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. A preparation method of a molybdenum dioxide nanowire/nanosheet thin film array with good electrocatalytic hydrogen evolution performance is characterized by comprising the following steps:

weighing 0.6-0.8g of ammonium molybdate in a beaker by adopting a traditional hydrothermal synthesis process, then adding only 0.2-0.3mL of 30% hydrogen peroxide or simultaneously adding 0.2-0.3mL of 30% hydrogen peroxide and 0.1-0.3mL of absolute ethyl alcohol, adding deionized water to 30mL, stirring until the solution is completely dissolved, then placing the solution in a polytetrafluoroethylene inner container, placing a 2-4cm molybdenum net in the polytetrafluoroethylene inner container, placing the polytetrafluoroethylene inner container in a metal reaction kettle and screwing down, placing the polytetrafluoroethylene inner container in a hydrothermal oven for hydrothermal reaction, preserving the temperature for 6-15h at the temperature of 150-.

2. The method for preparing molybdenum dioxide nanowire/nanosheet thin film array as recited in claim 1, wherein the precursor ammonium molybdate concentration is from 0.01618 to 0.02158M/L.

3. The preparation method of the molybdenum dioxide nanowire/nanosheet thin film array as defined in claim 1, wherein the hydrogen peroxide concentration in step 1 is 0.06526-0.09790M/L.

4. The method for preparing the molybdenum dioxide nanowire/nanosheet thin film array as defined in claim 1, wherein the hydrothermal reaction has a hydrothermal temperature of 170-210 ℃ and a hydrothermal reaction time of 8-12 h.