METHOD FOR SYNTHESIZING INTERGROWN TWIN Ni2Mo6S6O2/MoS2 TWO-DIMENSIONAL NANOSHEET

Abstract

A method for synthesizing an intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet with exposed (00L) crystal planes is disclosed. An Ni-Mo bonded precursor is formed by using an ion insertion method to restrict Ni ions to be located in a lattice matrix of a Mo-based compound; a dinuclear metal sulfide Ni.sub.2Mo.sub.6S.sub.6O.sub.2 is formed by precisely adjusting and controlling a concentration of a sulfur atmosphere and utilizing a reconstruction effect of Ni element in the lattice matrix of the Mo-based compound; and meanwhile, a growth direction of Ni.sub.2Mo.sub.6S.sub.6O.sub.2 is precisely adjusted and controlled by using a method for growing a single crystal in a limited area, so that Ni.sub.2Mo.sub.6S.sub.6O.sub.2 is grown, taking a single crystal MoS.sub.2 as a growth template, with the single crystal MoS.sub.2 alternately along a crystal plane (110) of the single crystal MoS.sub.2, so as to form a twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet in which Ni.sub.2Mo.sub.6S.sub.6O.sub.2and MoS.sub.2 are intergrown.

Claims

1. A method for synthesizing an intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet with exposed (00L) crystal planes, comprising: using an ion insertion method to restrict Ni ions to located in a lattice matrix of a Mo-based compound to form an Ni-Mo bonded precursor; precisely adjusting and controlling a concentration of a sulfur atmosphere to form a dinuclear metal sulfide Ni.sub.2Mo.sub.6S.sub.6O.sub.2; and meanwhile, using a method for growing a single crystal in a limited area to precisely adjust and control a growth direction of Ni.sub.2Mo.sub.6S.sub.6O.sub.2, wherein the Ni.sub.2Mo.sub.6S.sub.6O.sub.2 is grown, and a single crystal MoS.sub.2 is taken as a growth template, with the single crystal MoS.sub.2 alternately along a crystal plane (110) of the single crystal MoS.sub.2, to form a twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2 /MoS.sub.2 two-dimensional nanosheet, wherein the Ni.sub.2Mo.sub.6S.sub.6O.sub.2 and the MoS.sub.2 are intergrown in the twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet.

2. The method according to claim 1, comprising the steps of: 1) obtaining a first solution, by dissolving a molybdenum source and a nickel source in a H.sub.2O.sub.2 aqueous solution, and heating at a constant temperature until the molybdenum source and the nickel source are completely dissolved; wherein a Mo: Ni molar ratio of the molybdenum source and the nickel source is 1:1-1:2, a mass percentage of the H.sub.2O.sub.2 aqueous solution is 1-10 wt. %, and a temperature of the heating is 60-90° C.; 2) obtaining a second saturated solution containing a large amount of undissolved soluble salt solids, by adding a soluble salt into pure water under heating to obtain a first mixture, and stirring, and stopping the heating and stirring after a crystallization occurs above the first mixture and cooling the first mixture in ice water; wherein the soluble salt comprises sodium chloride, potassium chloride, sodium sulfate and potassium sulfate; 3) obtaining a second mixture, by mixing and stirring the first solution, the second solution, and all the undissolved soluble salt solids of step 2); 4) obtaining a dry solid, by placing the second mixture in liquid nitrogen for freezing and then placing the second mixture in a vacuum freeze dryer for vacuum freeze-drying for 12-48 hours, wherein the dry solid obtained is placed in a first porcelain boat, and then the first porcelain boat is placed in a center of a tube furnace, and a second porcelain boat containing a sulfur source is placed at an uptake port of the first porcelain boat, and a distance between the first porcelain boat and the second porcelain boat is precisely adjusted to be 3-4 cm; 5) introducing inert gas into the tube furnace, adjusting and controlling a flow rate of the inert gas to be 10-25 mL/min, and raising a temperature to a target temperature for constant temperature calcination; wherein a temperature raising rate is 1-10° C./min, the target temperature is 300-50° C., and a constant temperature calcination time is 1-10 hours; and 6) taking out the first porcelain boat after a vulcanization is completed, and washing a sample in the first porcelain boat with pure water and ethanol and then drying at room temperature, wherein a resulting product is the intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet.

3. The method according to claim 2, wherein the molybdenum source comprises molybdenum powder, molybdenum trioxide, molybdenum dioxide, ammonium molybdate and molybdenum acetylacetonate; and the nickel source comprises nickel nitrate, nickel acetylacetonate and nickel chloride.

4. The method according to claim 2, wherein in step 2), a mass of the soluble salt is 10-50 g, a volume of the pure water is 5-30 mL, and the heating a temperature of the heating is 50-100° C.

5. The method according to claim 2, wherein in step 3), a volume of the first pipetting solution is 0.05-0.2 mL, and a volume of the second pipetting solution is 0.5-2 mL.

6. The method according to claim 2, wherein in step 4), the sulfur source comprises thiourea and elemental sulfur, and a mass of the sulfur source is 10-40 g.

7. The method according to claim 2, wherein in step 5), the inert gas comprises nitrogen and argon.

8. A method of electrocatalytic water decomposition in a hydrogen evolution reaction, comprising the step of using the intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet with the exposed (00L) crystal planes obtained by the method according to claim 1 as a catalyst in the electrocatalytic water decomposition in the hydrogen evolution reaction.

9. The method according to claim 8, wherein the method for synthesizing the intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet with exposed (00L) crystal planes comprises the steps of: 1) obtaining a first solution, by dissolving a molybdenum source and a nickel source in a H.sub.2O.sub.2 aqueous solution, and heating at a constant temperature until the molybdenum source and the nickel source are completely dissolved; wherein a Mo: Ni molar ratio of the molybdenum source and the nickel source is 1:1-1:2, a mass percentage of the H.sub.2O.sub.2 aqueous solution is 1-10 wt. %, and a temperature of the heating is 60-90° C.; 2) obtaining a second saturated solution containing a large amount of undissolved soluble salt solids, by adding a soluble salt into pure water under heating to obtain a first mixture, and stirring, and stopping the heating and stirring after a crystallization occurs above the first mixture and cooling the first mixture in ice water; wherein the soluble salt comprises sodium chloride, potassium chloride, sodium sulfate and potassium sulfate; 3) obtaining a second mixture, by mixing and stirring the first solution, the second solution, and all the undissolved soluble salt solids of step 2); 4) obtaining a dry solid, by placing the second mixture in liquid nitrogen for freezing and then placing the second mixture in a vacuum freeze dryer for vacuum freeze-drying for 12-48 hours, wherein the dry solid obtained is placed in a first porcelain boat, and then the first porcelain boat is placed in a center of a tube furnace, and a second porcelain boat containing a sulfur source is placed at an uptake port of the first porcelain boat, and a distance between the first porcelain boat and the second porcelain boat is precisely adjusted to be 3-4 cm; 5) introducing inert gas into the tube furnace, adjusting and controlling a flow rate of the inert gas to be 10-25 mL/min, and raising a temperature to a target temperature for constant temperature calcination; wherein a temperature raising rate is 1-10° C./min, the target temperature is 300-500° C., and a constant temperature calcination time is 1-10 hours; and 6) taking out the first porcelain boat after a vulcanization is completed, and washing a sample in the first porcelain boat with pure water and ethanol and then drying at room temperature, wherein a resulting product is the intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet.

10. The method according to claim 9, wherein the molybdenum source comprises molybdenum powder, molybdenum trioxide, molybdenum dioxide, ammonium molybdate and molybdenum acetylacetonate; and the nickel source comprises nickel nitrate, nickel acetylacetonate and nickel chloride.

11. The method according to claim 9, wherein in step 2), a mass of the soluble salt is 10-50 g, a volume of the pure water is 5-30 mL, and a temperature of the heating is 50-100° C.

12. The method according to claim 9, wherein in step 3), a volume of the first solution is 0.05-0.2 mL, and a volume of the second solution is 0.5-2 mL.

13. The method according to claim 9, wherein in step 4), the sulfur source comprises thiourea and elemental sulfur, and a mass of the sulfur source is 10-40 g.

14. The method according to claim 9, wherein in step 5), the inert gas comprises nitrogen and argon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIGS. 1A-1C are scanning electron microscope micrographs of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 at three different scales;

[0024] FIG. 2 is an atomic force microscope micrograph of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2;

[0025] FIG. 3 is an X-ray diffraction fast-scan (with a scanning speed of 10°/min) spectrum of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2;

[0026] FIG. 4 is an X-ray diffraction fast-scan (with a scanning speed of 0.1°/min) spectrum of Ni.sub.2Mo.sub.6S.sub.6O/MoS.sub.2;

[0027] FIG. 5 is an electron diffraction spectrum of a selected area of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2;

[0028] FIG. 6 is a graph of linear scanning for Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2, NiS.sub.2 and MoS.sub.2;

[0029] FIG. 7 is a graph of linear scanning for Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 and PVC (20%); and

[0030] FIG. 8 is a graph of multi-step constant current of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 and Pt/C (20%

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following is a further description of the present invention, but not a limitation of the present invention.

Embodiment 1

[0032] A method for synthesizing an intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet with exposed (00L) crystal planes, the method includes the steps of:

[0033] 1) obtaining a solution A, by dissolving a molybdenum source and a nickel source with a molar ratio of Mo: Ni of 1:1.5 in a H.sub.2O.sub.2 aqueous solution with a mass ratio of 5% wt. and heating at a constant temperature of 60° C. until the molybdenum source and the nickel source are completely dissolved;

[0034] 2) obtaining a saturated solution B containing a large amount of undissolved soluble salt solids, by adding 20 g of a soluble salt into 15 mL, of pure water and heating to 60° C. and continuously stirring and stopping the heating and stirring after crystallization occurs above the mixture and cooling the mixture in ice water;

[0035] 3) obtaining a mixture C, by mixing and stirring 0.1 mL of the solution A, 1 mL of the solution B, and all undissolved soluble salt solids of step 2);

[0036] 4) obtaining a dry solid, by placing the mixture C in liquid nitrogen for freezing and then placing the mixture C in a vacuum freeze dryer for vacuum freeze-drying for 24 hours, wherein the obtained dry solid is placed in a porcelain boat A, and then the porcelain boat A is placed in the center of a tube furnace, and a porcelain boat B containing 20 g of a sulfur source is placed at an uptake of the porcelain boat A, the distance between the porcelain boat A and the porcelain boat B is precisely adjusted to be 3.5 cm, so that the concentration of the sulfur source above the porcelain boat A is moderate to prevent the excessive concentration of the sulfur source from destroying the Ni-Mo structure to form separate NiS.sub.2 and MoS.sub.2;

[0037] 5) introducing inert gas into the tube furnace, wherein a flow rate of the inert gas is 15 mL/thin, and the temperature is raised to 400° C. with a rate of 5° C./min and is kept for 5 hours; and

[0038] 6) taking out the porcelain boat A after the vulcanization is completed, and washing the sample in the porcelain boat A with pure water and ethanol and then drying at room temperature, wherein the resulting product is an intergrown twin Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet, the prepared Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 is in form of a two-dimensional nanosheet (as shown in FIGS. 1A-1C), has an average thickness of about 4.3 nm (as shown in FIG. 2), and has an intergrown twin phase structure of Ni.sub.2Mo.sub.6S.sub.6O.sub.2 and MoS.sub.2 with exposed (00L) crystal planes (such as FIG. 3, FIG. 4 and FIG. 5).

Embodiment 2

[0039] Referring to Embodiment 1, Embodiment 2 is different from Embodiment 1 in that, the mass ratio of the molybdenum source to the nickel source is 1:1.5-1:2, the mass percentage of the H.sub.2O.sub.2 aqueous solution is 5-10%, and the heating temperature is 60-90° C.

Embodiment 3

[0040] Referring to Embodiment 1, Embodiment 3 is different from Embodiment 1 in that, the mass of the soluble salt is 20-50 g, the volume of the pure water is 15-30 mL, and the heating temperature is 60-100° C.

Embodiment 4

[0041] Referring to Embodiment 1, Embodiment 4 is different from Embodiment 1 in that, the volume of the pipetting solution A is 0.1-0.2 mL, and the volume of the pipetting solution B is 1-2 mL.

Embodiment 5

[0042] Referring to Embodiment 1, Embodiment 5 is different from Embodiment 1 in that, the vacuum freeze-drying time is 24-48 hours, the mass of the sulfur source is 20-40 g, and the distance between the porcelain boat A, and the porcelain boat B is precisely adjusted to be 3.5-4 cm.

Embodiment 6

[0043] Referring to Embodiment 1, Embodiment 6 is different from Embodiment 1 in that, the flow rate of the inert gas is 15-25 mL/min, the temperature raising rate is 5-10° C./min, the target temperature is 400-500° C., and the constant temperature time is 5-10 hours,

Application Example 1

[0044] The Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet obtained in Embodiment 1 was carried. on a carbon cloth as a catalytic electrode. The Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet catalytic electrode and the NiS.sub.2 and MoS.sub.2 catalytic materials synthesized under the same conditions were linearly scanned respectively, and the specific steps are as follows.

[0045] A three-electrode configuration was used, with the catalytic electrode (Ni.sub.2Mo.sub.6S.sub.6O.sub.2, MoS.sub.2) as a working electrode, Ag/AgCl as a reference electrode, and platinum as a counter electrode. The electrolyte is an aqueous solution of 1 mol/L sodium hydroxide, The linear scanning was performed under the condition of 10 mV/s. The comparison of the results of the linear sweep voltammetry (LSV) shows that the HER performance of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 is stronger than that of NiS.sub.2 and MoS.sub.2 (FIG. 6), which indicates that Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 has an active site different from that of NiS.sub.2 and MoS.sub.2 (the active site of MoS.sub.2 is Mo-S, the active site of NiS.sub.2 is Ni-S), and further indicates that the main active site of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 is in Ni.sub.2Mo.sub.6S.sub.6O.sub.2 instead of MoS.sub.2, The HER performance of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 better than that of MoS.sub.2 proved that the introduction of Ni into MoS.sub.2 can effectively improve the performance of MoS.sub.2.

Application Example 2

[0046] The Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet obtained in Embodiment 1 was carried on a carbon cloth as a catalytic electrode. The Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet catalytic electrode and a commercial platinum carbon (20%) electrode were subjected to a linear scanning test, and the specific steps are as follows.

[0047] A three-electrode configuration was used, with the Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet catalytic electrode and the commercial platinum carbon (20%) catalyst as a working electrode, Ag/AgCl as a reference electrode, and platinum as a counter electrode. The electrolyte is an aqueous solution of 1 mol/L sodium hydroxide. The linear scanning was performed under the condition of 10 mV/s. The comparison of the results of the linear sweep voltammetry (LSV) shows that the initial potential of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 is close to that of Pt/C (20%) (FIG. 7), and as the overpotential increases, the increase of the reaction current of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 is much larger than that of Pt/C (20%), and finally Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 exhibits a HER activity superior to that of Pt/C (20%) at a large overpotential.

Application Example 3

[0048] The Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet obtained in Embodiment 1 was carried on a carbon cloth as a catalytic electrode. The Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet catalytic electrode and a commercial platinum carbon (20%) electrode were subjected to a step constant current test, and the specific steps are as follows.

[0049] A three-electrode configuration was used, with the Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 two-dimensional nanosheet catalytic electrode and the commercial platinum carbon (20%) catalyst as a working electrode, Ag/AgCl as a reference electrode, and platinum as a counter electrode. The electrolyte is an aqueous sodium of 1 mol/L hydroxide solution. The step constant current test is performed. under the conditions of 10 mA/cm.sup.2, 20 mA/cm.sup.2, 50 mA/cm.sup.2, 100 mA/cm.sup.2 and 200 mA/cm.sup.2, respectively, and each test period lasts for 60 seconds. The step constant current curve (FIG. 8) shows that Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 has a superior HER activity: at a current density of 250 mA/cm.sup.−2, Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 has an overpotential of 0.09 V, which is close to the overpotential of Pee: (20%) which is −0.01 V; as the current density increases, the overpotential of Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 and the overpotential of Pt/C (20%) gradually decrease, and finally at the current density of greater than 50 mA/cm.sup.−2, it shows that Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 has an advantage of having an overpotential smaller than that of Pt/C (20%). Therefore, in the current industry for producing hydrogen by electrolyzing water, it is required to evaluate the HER activity of the catalyst when the current density is greater than 100 mA/cm.sup.−2, Ni.sub.2Mo.sub.6S.sub.6O.sub.2/MoS.sub.2 exhibits the activity and the cheapness superior to that of Pt/C (20%).

[0050] The above description are the preferred embodiments of the present invention. It should be noted that, several improvements and changes can be made by those of ordinary skill in the art without departing from the inventive concept of the present invention, all of which belong to the scope of protection of the present invention.