CN113249753B - Molybdenum sulfide@cobalt-MOF/NF hydrogen evolution material and in situ synthesis method and application - Google Patents

Abstract

The invention relates to a molybdenum sulfide @ cobalt-MOF/NF hydrogen evolution material, an in-situ synthesis method and application, wherein the method comprises the following steps: preparing a mixed aqueous solution A of 2-methylimidazole and cobalt nitrate hexahydrate; placing the foam liquid into the mixed aqueous solution A prepared in S1, standing and soaking to obtain Co-MOF/NF; mixing ammonium molybdate hydrate, sodium sulfide nonahydrate and deionized water to obtain a mixed solution B; transferring Co-MOF/NF into the mixed solution B, and obtaining MoS after constant potential electrodeposition reaction₂@ Co-MOF/NF. Compared with the prior art, the method increases the specific surface area of the material, improves the contact area of the material and water, facilitates the preparation of hydrogen, improves the nanostructure of the material, and improves the hydrogen evolution performance and stability of the material by self-loading the flaky Co-MOF on the NF.

Description

Molybdenum sulfide@cobalt-MOF/NF hydrogen evolution material and in situ synthesis method and application

technical field

The invention relates to the technical field of hydrogen energy, in particular to a molybdenum sulfide@cobalt-MOF/NF hydrogen evolution material and an in-situ synthesis method and application.

Background technique

With the depletion of fossil fuels, various new energy sources are continuously developed and utilized. As a renewable secondary energy, hydrogen energy has a wide range of sources, high calorific value, cleanliness and good combustion stability. It is a new generation of widely used energy carriers after non-renewable energy sources such as fossil fuels.

Electrocatalytic water splitting consists of an oxygen evolution reaction (OER) and a hydrogen evolution reaction (HER), and HER is considered an efficient technology for the production of high-purity hydrogen (H ₂ ) due to its sustainability and carbon-free emissions. A great deal of work has been devoted to elucidating the cost-effective HER performance of electrolysis in acidic electrolytes, focusing on the preparation of high-performance electrocatalysts to reduce dynamic overpotentials. However, few electrocatalysts remain stable for HER performance in strongly acidic electrolytes such as 0.5MH ₂ SO ₄ . Meanwhile, in alkaline solutions, less material is available for high-energy radiation, which requires the ability to overcome a higher energy barrier compared to acidic electrolytes.

In general, highly active HER electrocatalysts require several features: (1) inherently high specific surface area, (2) high electrical conductivity and fast electron transfer pathways, and (3) large number of active sites and fast mass transport pathways (including transport of reaction substrates and diffusion of gaseous products). Although Pt and Ru/Ir-based composites are considered as state-of-the-art electrocatalysts for HER and OER, their high cost and scarcity severely hinder large-scale applications. Therefore, much research effort is devoted to developing earth-abundant alternatives with high efficiency and stability.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a molybdenum sulfide@cobalt-MOF/NF hydrogen evolution material and in-situ synthesis method and application in order to solve the above problems, the overall preparation process has low cost of raw materials, the preparation method is environmentally friendly, and the preparation method is simple. The material has good hydrogen evolution effect in alkaline solution.

The object of the present invention is achieved through the following technical solutions:

The first object of the present invention is to protect a method for in-situ synthesis of MoS ₂ @Co-MOF/NF hydrogen evolution material, comprising the following steps:

S1: prepare a mixed aqueous solution A of 2-methylimidazole and cobalt nitrate hexahydrate;

S2: the foam liquid is placed in the mixed aqueous solution A prepared in S1, and the Co-MOF/NF is obtained after standing and soaking;

S3: Mix ammonium molybdate hydrate, sodium sulfide nonahydrate with deionized water, adjust the pH of the solution to the target value, and obtain mixed solution B;

S4: Move Co-MOF/NF into the above mixed solution B, and obtain MoS ₂ @Co-MOF/NF after potentiostatic electrodeposition reaction.

Further, the preparation process of the mixed aqueous solution A described in S1 is: mixing 2-methylimidazole, cobalt nitrate hexahydrate and deionized water, and performing magnetic stirring to obtain the mixed solution A;

The molar ratio of described 2-methylimidazole and cobalt nitrate hexahydrate is 1:1, the molar ratio of described 2-methylimidazole and the volume of water is 1mmol:30mL, the molar ratio of cobalt nitrate hexahydrate and water The volume ratio of 1 mmol: 50 mL. Different contents of 2-methylimidazole and cobalt nitrate hexahydrate will generate MOFs with different structures after standing, and the best ratio should be selected.

Further, the stirring time described in S1 was 30 min, and a purple mixed solution A was obtained after stirring.

Further, in S2, deionized water and anhydrous ethanol were used to rinse the nickel foam respectively, repeated three times, and the dried nickel foam was soaked in solution A, the soaking temperature was room temperature, and the soaking time was 10h. The nickel foam was rinsed twice with absolute ethanol and deionized water, respectively, and dried in a vacuum oven overnight at a temperature of 60°C. The loading amount of methylimidazole and cobalt nitrate hexahydrate in the nickel foam is 10wt% to 20wt%.

Further, the molar ratio of Mo and S in the mixed solution B in S3 is 1:4, and the ratio of the molar amount of sodium sulfide nonahydrate to the volume of deionized water is 2mmol:50mL.

Further, in S3, the pH is adjusted to the target value by adding nitric acid.

Further, in S3, the PH is determined to be adjusted to the target value through the change of the color of the solution, and the sign of the color change is that the solution changes from yellow to reddish brown.

Further, the potentiostatic range of the potentiostatic electrodeposition in S4 is -0.8V～-1.0V, and the time range of the potentiostatic electrodeposition is 1200s～7200s.

The second object of the present invention is to protect a MoS ₂ @Co-MOF/NF hydrogen evolution material obtained by the above preparation method.

The third object of the present invention is to protect the application of a MoS ₂ @Co-MOF/NF hydrogen evolution material in electrocatalytic hydrogen evolution reaction.

Further, the MoS ₂ @Co-MOF/NF hydrogen evolution material was used as the working electrode in the electrocatalytic hydrogen evolution reaction.

Compared with the prior art, the technical advantages of the present invention are:

1) The Tafel slope and overpotential of the hydrogen evolution material prepared in this technical solution are low, so that the energy barrier to be broken through for hydrogen evolution is low, the hydrogen conversion rate is high, the hydrogen rate is fast, the cost of raw materials is low, the preparation method is environmentally friendly, and the preparation method is Simple, the material has good hydrogen evolution effect in alkaline solution, and is expected to be developed for industrialization.

2) In the present invention of the hydrogen evolution material, the foamed nickel used is a sound-absorbing "porous metal" with excellent three-dimensional full-through mesh structure performance, the porosity of the foamed nickel is about 95%, and water or gas can flow unimpeded. The nickel skeleton is hollow and interconnected in a metallurgical state, and has the advantages of good stability, high porosity, thermal shock resistance, low bulk density and large specific surface area.

3) In the technical solution, by self-supporting the sheet-like Co-MOF on NF, the specific surface area of the material is increased, the contact area between the material and water is increased, the hydrogen gas is easier to obtain, and the nanostructure of the material is improved at the same time. , which improves the hydrogen evolution performance and stability of the material.

Detailed ways

As a part of the concept of this technical solution, the nickel foam used in this technical solution is a commercialized metal functional material with three-dimensional openings, pores and metal skeleton interconnected, and has a large electrochemical reaction interface. It has great application prospects.

和优异的热力学稳定性。然而，单个的MoS₂由于活性位点暴露较少、导电性较差，因此本技术方案进一步提高这些基于TMDs的催化剂的催化性能以满足实际应用。As part of the concept of this technical solution, in order to solve the above problems and further improve the electrochemical activity, several strategies have been proposed to address the above-mentioned key problems, such as the use of transition metal dichalcogenides (TMDs) as the catalytic cathode for HER, because it has similar Catalytic properties of Pt with near-zero free energy hydrogen adsorption

and excellent thermodynamic stability. However, single _MoS has less exposed active sites and poor conductivity, so this technical scheme further improves the catalytic performance of these TMDs-based catalysts to meet practical applications.

The present invention will be described in detail below in conjunction with specific embodiments, but by no means limit the present invention.

Various raw materials used in each embodiment of the present invention are commercially available unless otherwise specified.

Example 1

The above-mentioned hydrogen evolution material is prepared by the preparation method of the following steps:

Dissolve 1 mmol of 2-methylimidazole and 1 mmol of cobalt nitrate hexahydrate in 30 mL and 50 mL of deionized water, respectively, and stir them in a magnetic stirrer for 30 min after mixing until there are no solid particles in the solution and the color is purple. The 1mm×4mm×1mm nickel foam was soaked at room temperature for 10h, and the soaked Co-MOF/NF was washed twice with absolute ethanol and deionized water, respectively, and vacuumized at 60 °C overnight to dry; 0.07mmol of tetrahydrate molybdic acid was Ammonium and 2mmol of sodium sulfide nonahydrate were dissolved in 50mL of deionized water, and 0.1mL of nitric acid was added dropwise to adjust the pH, and the solution changed from yellow to reddish-brown; the dried Co-MOF/NF was used as the working electrode, and the constant temperature was carried out on the chi760e electrochemical workstation. Potential electrodeposition, voltage: -0.8V; electrodeposition time: 1200s. Finally, MoS ₂ @Co-MOF/NF hydrogen evolution material was obtained.

Application Example 1

The MoS ₂ @Co-MOF/NF hydrogen evolution material of Example 1 was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(1) MoS ₂ @Co-MOF/NF hydrogen evolution material was washed twice with deionized water and isopropanol, respectively, and was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(2) 1.0M potassium hydroxide solution was prepared as the electrocatalytic electrolyte, nitrogen was introduced to drive away the air, and then MoS ₂ @Co-MOF/NF, Ag/AgCl electrode, and platinum electrode were used as the working electrode and the reference electrode, respectively. The electrode and the counter electrode were connected to an electrochemical workstation, and the electrocatalytic hydrogen evolution performance of the electrode material was measured in the electrolyte. This material has a Tafel slope of 126.24 mV dec ^-1 and an overpotential of 255 mV at a current density of 10 mA cm ^-2 .

Example 2

The above-mentioned hydrogen evolution material is prepared by the preparation method of the following steps:

Dissolve 1 mmol of 2-methylimidazole and 1 mmol of cobalt nitrate hexahydrate in 30 mL and 50 mL of deionized water, respectively, and stir them in a magnetic stirrer for 30 min after mixing until there are no solid particles in the solution and the color is purple. The 1mm×4mm×1mm nickel foam was soaked at room temperature for 10h, and the soaked Co-MOF/NF was washed twice with absolute ethanol and deionized water, respectively, and vacuumized at 60 °C overnight to dry; 0.07mmol of tetrahydrate molybdic acid was Ammonium and 2mmol of sodium sulfide nonahydrate were dissolved in 50mL of deionized water, and 0.1mL of nitric acid was added dropwise to adjust the pH, and the solution changed from yellow to reddish-brown; the dried Co-MOF/NF was used as the working electrode, and the constant temperature was carried out on the chi760e electrochemical workstation. Potential electrodeposition, voltage: -0.8V; electrodeposition time: 2400s. Finally, MoS ₂ @Co-MOF/NF hydrogen evolution material was obtained.

Application Example 2

The MoS ₂ @Co-MOF/NF hydrogen evolution material of Example 2 was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(1) MoS ₂ @Co-MOF/NF hydrogen evolution material was washed twice with deionized water and isopropanol, respectively, and was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(2) 1.0M potassium hydroxide solution was prepared as the electrocatalytic electrolyte, nitrogen was introduced to drive away the air, and then MoS ₂ @Co-MOF/NF, Ag/AgCl electrode, and platinum electrode were used as the working electrode and the reference electrode, respectively. The electrode and the counter electrode were connected to an electrochemical workstation, and the electrocatalytic hydrogen evolution performance of the electrode material was measured in the electrolyte. This material has a Tafel slope of 38.33 mV dec ^-1 and an overpotential of 165 mV at a current density of 10 mA cm ^-2 . And the LSV curve after 1000 cycles of CV test has little deviation from the LSV curve before CV test, indicating that the material has good stability.

Example 3

The above-mentioned hydrogen evolution material is prepared by the preparation method of the following steps:

Dissolve 1 mmol of 2-methylimidazole and 1 mmol of cobalt nitrate hexahydrate in 30 mL and 50 mL of deionized water, respectively, and stir in a magnetic stirrer for 30 min after mixing until there are no solid particles in the solution and the color is purple. 1mm × 4mm × 1mm nickel foam was soaked at room temperature for 10 hours, the soaked Co-MOF/NF was washed twice with absolute ethanol and deionized water, respectively, and vacuumized at 60 °C overnight to dry; 0.07 mmol of tetrahydrate molybdic acid was Ammonium and 2mmol of sodium sulfide nonahydrate were dissolved in 50mL of deionized water, and 0.1mL of nitric acid was added dropwise to adjust the pH, and the solution changed from yellow to reddish-brown; the dried Co-MOF/NF was used as the working electrode, and the constant temperature was carried out on the chi760e electrochemical workstation. Potential electrodeposition, voltage: -0.8V; electrodeposition time: 7200s. Finally, MoS ₂ @Co-MOF/NF hydrogen evolution material was obtained.

Application Example 3

The MoS ₂ @Co-MOF/NF hydrogen evolution material of Example 3 was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(1) MoS ₂ @Co-MOF/NF hydrogen evolution material was washed twice with deionized water and isopropanol, respectively, and was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(2) 1.0M potassium hydroxide solution was prepared as the electrocatalytic electrolyte, nitrogen was introduced to drive away the air, and then MoS ₂ @Co-MOF/NF, Ag/AgCl electrode, and platinum electrode were used as the working electrode and the reference electrode, respectively. The electrode and the counter electrode were connected to an electrochemical workstation, and the electrocatalytic hydrogen evolution performance of the electrode material was measured in the electrolyte. This material has a Tafel slope of 96.12 mV dec ^-1 and an overpotential of 249 mV at a current density of 10 mA cm ^-2 .

Comparative Example 1

2-Methylimidazole 1.0mmol

Cobalt nitrate hexahydrate 1.0mmol

Deionized water 80.0ml

The above-mentioned hydrogen evolution material is prepared by the preparation method of the following steps:

Dissolve 10 mmol of 2-methylimidazole and 1 mmol of cobalt nitrate hexahydrate in 30 mL and 50 mL of deionized water, respectively, and stir in a magnetic stirrer for 30 min after mixing until there are no solid particles in the solution and the color is purple. 1mm × 4mm × 1mm nickel foam was soaked at room temperature for 10h, the soaked Co-MOF/NF was washed twice with absolute ethanol and deionized water, respectively, and dried at 60 °C under vacuum overnight; the hydrogen evolution of Co-MOF/NF was obtained. Material.

Application Example 1

The Co-MOF/NF hydrogen evolution material of Comparative Example 1 was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction after drying.

(1) Prepare a 1.0M potassium hydroxide solution as the electrocatalytic electrolyte, introduce nitrogen to drive away the air, and then use Co-MOF/NF, Ag/AgCl electrodes, and platinum electrodes as the working electrode, reference electrode, pair The electrode was connected to an electrochemical workstation, and the electrocatalytic hydrogen evolution performance of the electrode material was measured in the electrolyte. This material has a Tafel slope of 90.19 mV dec ^-1 and an overpotential of 275 mV at a current density of 10 mA cm ^-2 . Co-MOF alone has higher specific surface area and porosity, but MoS ₂ supported by electrodeposition can further improve the electrochemical performance of the sample, so the electrochemical performance of this comparative case is reduced compared to the practical case.

Comparative Example 2

The above-mentioned hydrogen evolution material is prepared by the preparation method of the following steps:

Dissolve 0.07 mmol of ammonium molybdate tetrahydrate and 2 mmol of sodium sulfide nonahydrate in 50 mL of deionized water, drop 0.1 mL of nitric acid to adjust the pH, and the solution changes from yellow to reddish-brown; the dried NF is used as the working electrode, and the chi760e electrochemical Workstation for potentiostatic electrodeposition, voltage: -0.8V; electrodeposition time: 2400s. Finally, MoS ₂ /NF hydrogen evolution material was obtained.

Application Comparative Example 2

The MoS ₂ /NF hydrogen evolution material of Comparative Example 2 was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(1) MoS ₂ /NF hydrogen evolution material was washed twice with deionized water and isopropanol, respectively, and was directly used as the working electrode in the electrocatalytic hydrogen evolution reaction without drying.

(2) Prepare a 1.0M potassium hydroxide solution as the electrocatalytic electrolyte, introduce nitrogen to drive off the air, and then use MoS ₂ /NF, Ag/AgCl electrodes, and platinum electrodes as working electrode, reference electrode, and counter electrode respectively. The electrochemical workstation was connected, and the electrocatalytic hydrogen evolution performance of the electrode material was measured in the electrolyte. This material has a Tafel slope of 148.15 mV dec ^-1 and an overpotential of 225 mV at a current density of 10 mA cm ^-2 .

Comparative Example 3

Mo-S/NF hydrogen evolution material in CN111359636A and its preparation method and application, the preparation method is: 1) mixing ammonium tetrathiomolybdate, thiourea and water, and ultrasonically dispersing to obtain a mixed solution; 2) mixing The solution is added to the reaction kettle, and nickel foam is placed in the reaction kettle as a carrier, and Mo-S/NF is obtained after hydrothermal reaction; 3) Mo-S/NF is calcined under anaerobic conditions to obtain Mo-S/NF -S/NF hydrogen evolution material. This material has a Tafel slope of 98 mV dec ^-1 and an overpotential of 225 mV at a current density of 10 mAcm ^-2 .

Compared with Comparative Example 3, this technical solution can obtain better electrochemical performance only by self-loading and electrodeposition. Through self-loading and electrodeposition, a sample wrapped with polyhedron can be formed, which greatly increases its active specific surface area. Improve the electrochemical performance of the sample.

The foregoing description of the embodiments is provided to facilitate understanding and use of the invention by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made, and the generic principles described herein can be applied to other embodiments without inventive step. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should all fall within the protection scope of the present invention.

Claims (5)

1. a method for in-situ synthesis of MoS ₂ @Co-MOF/NF hydrogen evolution material, is characterized in that, comprises the following steps: S1: prepare a mixed aqueous solution A of 2-methylimidazole and cobalt nitrate hexahydrate; S2: the foam liquid is placed in the mixed aqueous solution A prepared in S1, and the Co-MOF/NF is obtained after standing and soaking; S3: Mix ammonium molybdate hydrate, sodium sulfide nonahydrate with deionized water, adjust the pH of the solution to the target value, and obtain mixed solution B; S4: Move Co-MOF/NF into the above mixed solution B, and obtain MoS ₂ @Co-MOF/NF after potentiostatic electrodeposition reaction; The preparation process of the mixed aqueous solution A described in S1 is: mixing 2-methylimidazole, cobalt nitrate hexahydrate and deionized water, and performing magnetic stirring to obtain a mixed solution A; The molar ratio of described 2-methylimidazole and cobalt nitrate hexahydrate is 1:1, the molar ratio of described 2-methylimidazole and the volume of water is 1mmol:30mL, the molar ratio of cobalt nitrate hexahydrate and water The volume ratio of 1mmol: 50mL; In S3, the molar ratio of Mo and S in the mixed solution B is 1:4, and the ratio of the molar amount of sodium sulfide nonahydrate to the volume of deionized water is 2mmol:50mL; Adjust pH to target value by adding nitric acid in S3; In S3, it is determined to adjust the pH to the target value by the change of the color of the solution, and the sign of the color change is that the solution changes from yellow to reddish brown; The time range of potentiostatic electrodeposition was 1200s~7200, and the deposition voltage was -0.8V. 2. the method for a kind of in-situ synthesis of MoS ₂ @Co-MOF/NF hydrogen evolution material according to claim 1, is characterized in that, in S2, use deionized water, absolute ethanol successively to rinse nickel foam respectively, repeat three times , soak the dried nickel foam in solution A, the soaking temperature is room temperature, and the soaking time is 10h. After soaking, the nickel foam is washed twice with absolute ethanol and deionized water, and dried in a vacuum oven overnight. is 60°C. 3. MoS ₂ @Co-MOF/NF hydrogen evolution material obtained by the preparation method according to any one of claims 1 to 2. 4. the application of MoS ₂ @Co-MOF/NF hydrogen evolution material described in claim 3 in electrocatalytic hydrogen evolution reaction. 5. the application of a kind of MoS ₂ @Co-MOF/NF hydrogen evolution material according to claim 4 in electrocatalytic hydrogen evolution reaction, using described MoS ₂ @Co-MOF/NF hydrogen evolution material as electrocatalytic hydrogen evolution reaction the working electrode.