CN113215598B

CN113215598B - Bi-MoS for electro-catalytic synthesis of ammonia2Process for preparing nano composite material

Info

Publication number: CN113215598B
Application number: CN202110516511.9A
Authority: CN
Inventors: 周炎; 夏菡菡; 尤紫晗; 孙凤超; 王淑涛; 贾翠萍; 张军
Original assignee: China University of Petroleum East China
Current assignee: China University of Petroleum East China
Priority date: 2021-05-12
Filing date: 2021-05-12
Publication date: 2022-06-03
Anticipated expiration: 2041-05-12
Also published as: CN113215598A

Abstract

The invention relates to a Bi-MoS for electrocatalytic ammonia synthesis₂A method for preparing a nano composite material, which belongs to the technical field of nano materials; the Bi-MoS₂The nano composite material takes molybdenum disulfide as a substrate, and the bismuth nanocrystals are compounded on the molybdenum disulfide substrate; and compounding the bismuth nanocrystals with molybdenum disulfide nanosheets by using molybdenum disulfide as a substrate through hydrothermal reaction. The preparation process is simple and feasible, the cost is low, the environment is protected, the electrochemical activity can be shown under the condition of not using noble metal, the ammonia yield can reach 15 mu g h^‑1mg^‑1 _catThe Faraday efficiency can reach 25%.

Description

Bi-MoS for electrocatalytic ammonia synthesis2Process for preparing nano composite material

Technical Field

The invention relates to the field of electrocatalytic nitrogen reduction electrode materials, in particular to a main group metal Bi and metal sulfide MoS for electrocatalytic synthesis of ammonia₂A composite electrode material and a preparation method thereof.

Background

Ammonia plays an important role in production and life, is widely applied to the fields of fertilizers, textiles, pharmacy, plastics and the like, is one of the most abundant inorganic compounds in the world, and more than eighty percent of ammonia is used for preparing the fertilizers. Owing to the dipole moment of N.ident.N and the extremely high bond energy (940.95kJ mol)^-1) It is chemically inert, hindering the nitrogen fixation process.

In nature, the organism N₂The immobilization is carried out by a nitrogen-fixing enzyme under mild conditions. However, the efficiency is low and cannot be used for practical production. The industry relies principally on the Haber-Bosch process to utilise N in the presence of an iron-based catalyst₂And H₂High temperature (400-500 ℃) and high pressure (200-250 bar) to synthesize ammonia. This method not only requires huge energy consumption (1-3% energy consumption worldwide)) Also, a large amount of CO is produced₂Gas (per ton NH)₃Production of 1.5 tons of CO₂). Therefore, there is an urgent need to develop a new process that can replace the conventional Haber-Bosch process.

To date, researchers have made tremendous efforts in photocatalysis, electrocatalysis, and biological strategies in order to promote artificial nitrogen fixation. Use of heterogeneous catalysts with N at room temperature by means of renewable solar and wind energy₂And H₂Production of NH from O₃The electrochemical reduction process has great potential.

Competitive hydrogen evolution reaction exists in the electrocatalytic nitrogen reduction process, and active sites can more easily adsorb protons instead of N₂Making most catalysts very inefficient in faradaic efficiency (e.g., Pt-based, Rh-based, Ru-based, etc.). The extremely low selectivity is not sufficient to meet the demand for large-scale ammonia production, and therefore, new electrode materials are tried, and improvement of catalytic performance is a hot problem. In addition, CN112275298A discloses a bismuth sulfide composite potassium tantalate-niobate catalyst, a preparation method and an application of the catalyst, which have photocatalytic and piezoelectric catalytic nitrogen fixation properties. And N is bonded under ultrasonic vibration while nitrogen fixation is carried out through photocatalysis₂Conversion to NH₃. CN109908887A discloses a micro-oxidation conductive carbon black supported nano metal bismuth catalyst and application thereof, and the catalyst has the performance of electro-catalysis ammonia synthesis. The alkali metal ions are firstly found to be introduced into an electro-catalytic ammonia synthesis reaction system as a cocatalyst, so that the selectivity and activity of the metal bismuth catalyst in the electro-catalytic ammonia synthesis reaction are improved. CN112121827A discloses a high-efficiency electro-catalytic synthesis method of ammonia FeSe₂/MoSe₂Nanosheet and preparation method and application thereof. The catalyst has a large surface area to volume ratio and thus has excellent properties different from bulk materials. However, the existing methods all require complicated processes.

Because Bi has poor hydrogen evolution performance and is widely applied to photocatalytic nitrogen reduction, MoS is added₂Has been demonstrated to have NRR activity, and the synergistic effect of the two can promote NRR development. There are also patent documents on composite materials of molybdenum disulfide and bismuth, such as: CN110247038A discloses a Bi-component metal sulfide/graphene composite nano material and a preparation method thereof, wherein the composite material is prepared from Bi₂S₃Nanoparticles and MoS₂The nano sheets are compounded and uniformly loaded on the graphene. CN106311283A discloses a p-n heterojunction BiVO₄/MoS₂A preparation method of a composite photocatalyst. However, the composite material is mainly used in the field of lithium ion batteries or photocatalysis, and no report is found on the electrocatalytic synthesis of ammonia.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides Bi-MoS for synthesizing ammonia by electrocatalysis₂The nano composite material is synthesized by a hydrothermal method, and the composite material has obvious selectivity by controlling the technological process, so that the prepared composite electrode material has the purposes of high yield, high activity and good electrochemical performance. The preparation operation is simple, and complex equipment is not needed.

The technical scheme of the invention is as follows:

Bi-MoS for electrocatalytic ammonia synthesis₂Nanocomposite material of said Bi-MoS₂The nano composite material takes molybdenum disulfide as a substrate, and the bismuth nanocrystals are compounded on the molybdenum disulfide substrate.

According to the invention, the ammonia yield of the composite material can reach 15 mu g h^-1mg^-1 _cat。

According to the invention, preferably 0.5M K with a pH of 4 is used₂SO₄The Faraday efficiency of the composite material can reach 25 percent.

According to the invention, the above-described Bi-MoS for the electrocatalytic synthesis of ammonia₂The preparation method of the nano composite material comprises the following steps:

mixing MoS₂Dispersing in anhydrous glycol, and performing ultrasonic treatment; adding ethylene glycol solution and bismuth nitrate pentahydrate, stirring and then carrying out ultrasonic treatment to obtain mixed solution;

carrying out hydrothermal reaction on the mixed solution, centrifuging, washing and drying the obtained product to obtain Bi-MoS₂A nanocomposite material.

According to the invention, preferably, the MoS is₂In the process of dispersing in anhydrous glycol, the ratio of the mass amount of the molybdenum disulfide to the volume amount of the glycol is 5-15 mg: 5-15 ml; preferably, the ultrasonic time is 1-3 h.

According to the invention, preferably, in the process of adding the ethylene glycol solution and the bismuth nitrate pentahydrate, the volume dosage of the ethylene glycol and the molar dosage of the bismuth nitrate pentahydrate are 5-15 ml: 1-2 mmol; preferably, the stirring time is 8-12 h, and the ultrasonic time is 5-15 min.

According to the invention, the temperature of the hydrothermal reaction is preferably 160-200 ℃, and the time of the hydrothermal reaction is preferably 12-16 h.

According to the invention, preferably, said MoS₂The preparation method comprises the following steps:

dissolving sodium molybdate dihydrate and thiourea in deionized water, stirring, transferring into a stainless steel reaction kettle with a polytetrafluoroethylene lining, sealing, heating in an oven for reaction, naturally cooling to room temperature after the reaction is finished, washing with deionized water and ethanol, and vacuum drying to obtain MoS₂。

According to the invention, the molar ratio of sodium molybdate dihydrate to thiourea is preferably 1: (2-8), wherein the ratio of the molar amount of sodium molybdate dihydrate to the volume amount of deionized water is 1 mol: 25-50 ml.

According to the invention, preferably, the stirring time is 0.2-0.6 h, the heating reaction temperature is 180-220 ℃, and the heating reaction time is 12-24 h.

According to the invention, the vacuum drying temperature is preferably 60 ℃ and the time is preferably 12 h.

According to the invention, preferably, the Bi-MoS for the electrocatalytic synthesis of ammonia₂A preferred embodiment of the nanocomposite material comprises the steps of:

(1) dissolving 1mmol of sodium molybdate dihydrate and 2-8 mmol of thiourea in 25-50 ml of deionized water, stirring for 0.2-0.6 h, transferring into a stainless steel reaction kettle with a polytetrafluoroethylene lining, sealing, and heating in an oven at 180-220 ℃ for reaction for 12-24 h;

(2) after the reaction is finished, naturally cooling to room temperature, washing with deionized water and ethanol, and vacuum drying at 60 ℃ for 12h to obtain molybdenum disulfide;

(3) completely dispersing 5-15 mg of molybdenum disulfide in 5-15 ml of anhydrous ethylene glycol, and carrying out ultrasonic treatment for 1-3 h;

(4) then adding 5-15 ml of ethylene glycol solution and 1-2 mmol of bismuth nitrate pentahydrate, strongly stirring for 8-12 h, and then carrying out ultrasonic treatment for 5-15 min to obtain a mixed solution;

(5) transferring the mixed solution into a stainless steel reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction at the temperature of 160-200 ℃ for 12-16 h, centrifugally separating a product after the reaction is finished, washing with water and ethanol, and drying in vacuum to obtain Bi-MoS₂A nanocomposite material.

Bi-MoS of the invention₂The nano composite material has excellent electro-catalytic ammonia synthesis performance, 5mg of catalyst sample is dispersed into 900 mul of ethanol, 100 mul of Nafion solution is added to form uniform slurry, ultrasonic treatment is carried out for 1h, then 200 mul of mixed solution is dripped into pretreated carbon paper, and the loading concentration is 1mgcm^-2As a working electrode, an electrocatalytic ammonia synthesis test can be performed.

The LSV curve and i-t test of the invention were performed using CHI660E electrochemical workstation at pH 4 of 0.5M K₂SO₄The method is carried out in an electrolyte, Ag/AgCl (3M KCl) is used as a reference electrode, a Pt sheet is used as a counter electrode, and an electrode prepared by the catalyst is used as a working electrode.

The invention has the following beneficial effects:

1. the invention compounds Bi of main group elements with poor hydrogen evolution performance and molybdenum disulfide widely applied in electrochemistry for the first time. Due to MoS₂The invention takes the Bi nano-crystal as a substrate, adopts a two-step method to compound the Bi nano-crystal and the molybdenum disulfide, and the synergistic effect of the Bi nano-crystal and the molybdenum disulfide can promote the development of NRR.

2. The substrate used in the present invention is MoS₂The performance is stable and suitable for being used as a substrate, and experiments show that MoS₂Has good NRR catalytic activity.

3. The preparation process is simple and feasible, low in cost and environment-friendly. Can exhibit excellent electrochemical activity without using a noble metal.

4. Bi nanocrystals and MoS used in the present invention₂Compounding, improving the catalytic performance and obtaining Bi-MoS₂The nano composite material has excellent electro-catalysis ammonia synthesis performance, and the ammonia yield can reach 15 mu g h^-1 mg^-1 _cat。

5. Bi-MoS of the invention₂The electro-catalysis synthesis of ammonia by the nano composite material has good selectivity, and 0.5M K with pH 4 is used₂SO₄The Faraday efficiency of the electrolyte can reach 25 percent.

Drawings

FIG. 1 shows Bi-MoS prepared in example 2₂X-ray diffraction (XRD) pattern of the nanocomposite.

FIG. 2 is a TEM micrograph of pure molybdenum disulfide obtained in example 1.

FIG. 3 shows Bi-MoS obtained in example 2₂Transmission electron microscopy test photographs of the nanocomposites.

FIG. 4 shows Bi-MoS prepared in example 2₂Linear Scanning (LSV) profile of the nanocomposite.

FIG. 5 shows Bi-MoS prepared in example 2₂Ammonia yield and faraday efficiency plot of the nanocomposite.

FIG. 6 is a graph comparing the ammonia yield and Faraday efficiency of the composite materials obtained in Experimental example 3, example 2 and comparative examples 1-3.

Detailed Description

The present invention will be further described with reference to the following examples.

In the following examples, the main experimental reagents and instruments used are listed below:

bismuth nitrate pentahydrate (Bi (NO)₃)₂·5H₂O), Ethylene Glycol (EG), sodium molybdate dihydrate (Na)₂MoO₄·2H₂O), thiourea (CH)₄N₂S), absolute ethanol, Nafion (5 wt%), magnetic stirrer (Color liquid [ white ]]) Desk type high speed centrifuge (TG)16-WS), analytical electronic balance (BS210S), electrothermal forced air drying cabinet (DHG-9015A), ultrasonic cleaner (KQ2200B type), X-ray diffractometer (X' Pert PRO MPD), transmission electron microscope (JEM-2100(UHR), electrochemical workstation (CHI 660E).

Example 1 preparation of molybdenum disulfide

2mmol of sodium molybdate dihydrate and 8mmol of thiourea are dissolved in 44ml of deionized water and stirred for 0.5 h.

Transferring into a polytetrafluoroethylene stainless steel reaction kettle, sealing, and heating in an oven at 200 deg.C for 24 h.

Naturally cooling to room temperature, washing with deionized water and ethanol for 4 times, and vacuum drying at 60 deg.C for 12h to obtain molybdenum disulfide.

Example 2 Bi-MoS₂Preparation of nanocomposites

10mg of the molybdenum disulfide prepared in example 1 was completely dispersed in 10ml of anhydrous ethylene glycol, and after 2 hours of sonication, 5ml of an ethylene glycol solution and 1.4mmol of bismuth nitrate pentahydrate were added to obtain a mixed solution.

The mixed solution is stirred strongly for 12 hours, and is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction for 16 hours at 180 ℃ after ultrasonic treatment for 15 min.

Centrifuging the final product, washing with ethanol for 4 times, and vacuum drying to obtain Bi-MoS₂A nanocomposite material.

Example 3 Bi-MoS₂Preparation of nanocomposites

5mg of molybdenum disulfide prepared in example 1 was completely dispersed in 10ml of anhydrous ethylene glycol, and after 2 hours of sonication, 5ml of an ethylene glycol solution and 1mmol of bismuth nitrate pentahydrate were added to obtain a mixed solution.

The mixed solution is stirred strongly for 12 hours, and is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction for 16 hours at 160 ℃ after ultrasonic treatment for 15 min.

Example 4 Bi-MoS₂Preparation of nanocomposites

15mg of the molybdenum disulfide prepared in example 1 was completely dispersed in 10ml of anhydrous ethylene glycol, and after 2 hours of sonication, 15ml of an ethylene glycol solution and 2mmol of bismuth nitrate pentahydrate were added to obtain a mixed solution.

The mixed solution is stirred strongly for 12 hours, and is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction for 12 hours at 200 ℃ after ultrasonic treatment for 15 minutes.

Example 5 Bi-MoS₂Preparation of nanocomposites

10mg of the molybdenum disulfide prepared in example 1 was completely dispersed in 15ml of anhydrous ethylene glycol, and after 2 hours of sonication, 10ml of an ethylene glycol solution and 1.8mmol of bismuth nitrate pentahydrate were added to obtain a mixed solution.

The mixed solution is stirred strongly for 12 hours, and is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining for ultrasonic treatment for 15min to carry out hydrothermal reaction for 14 hours at the temperature of 170 ℃.

Comparative example 1 preparation of Bi-carbon Black (Bi-C)

10mg of carbon black was completely dispersed in 10ml of anhydrous ethylene glycol, and after two hours of sonication, 5ml of ethylene glycol solution and 1.4mmol of bismuth nitrate pentahydrate were added.

And centrifuging the final product, washing with ethanol for 4 times, and drying in vacuum to obtain Bi-C.

Comparative example 2 Fe-MoS₂Preparation of nanocomposites

10mg of the molybdenum disulfide prepared in example 1 was completely dispersed in 10ml of anhydrous ethylene glycol, and after 2 hours of sonication, 5ml of an ethylene glycol solution and 1.4mmol of iron nitrate nonahydrate were added to obtain a mixed solution.

Centrifuging the final product, washing with ethanol for 4 times, and vacuum drying to obtain Fe-MoS₂NanocompositeA material.

Comparative example 3, Co-MoS₂Preparation of nanocomposites

10mg of the molybdenum disulfide prepared in example 1 was completely dispersed in 10ml of anhydrous ethylene glycol, and after 2 hours of sonication, 5ml of an ethylene glycol solution and 1.4mmol of cobalt nitrate hexahydrate were added to obtain a mixed solution.

The mixed solution is stirred strongly for 12 hours, and is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction for 16 hours at 180 ℃ after ultrasonic treatment for 15 minutes.

Centrifuging the final product, washing with ethanol for 4 times, and vacuum drying to obtain Co-MoS₂A nanocomposite material.

Test example 1

XRD test: the Bi-MoS prepared in example 2 was used₂The nanocomposite samples were subjected to XRD testing as shown in fig. 1.

As is clear from FIG. 1, the X-ray diffraction peaks were found to be compatible with BiNCs and MoS₂Corresponding to the standard card of (1), and proving that the Bi-MoS is₂Successful synthesis of nanocomposites.

Transmission electron microscope: the pure molybdenum disulfide obtained in example 1 was subjected to transmission electron microscopy as shown in fig. 2; the Bi-MoS obtained in example 2 was used₂The nanocomposites were subjected to transmission electron microscopy as shown in FIG. 3. It can be known from fig. 2 and fig. 3 that the molybdenum disulfide synthesized by the above experimental method is flaky, and BiNCs and molybdenum disulfide are successfully compounded.

Test example 2

And (3) electrochemical performance testing: the Bi-MoS obtained in example 2 was used₂The nano composite material is assembled into an electrode to be tested in electrochemical performance under a three-electrode system, and the electrolyte is 0.5M K with pH of 4₂SO₄And (3) solution.

5mg of Bi-MoS₂Dispersing the nano composite material sample into 900 mul of ethanol, adding 100 mul of Nafion solution to form uniform slurry, performing ultrasonic treatment for 1h, and then dropwise coating 200 mul of mixed solution into the pretreated carbon paper with the loading concentration of 1mg cm^-2As a working electrode; Ag/AgCl (3M KCl) is used as a reference electrode, and a Pt sheet is used as a counter electrode; electrochemical work station with CHI660E at 0.5 pH 4M K₂SO₄The test was carried out in the electrolyte.

FIG. 4 shows Bi-MoS obtained in example 2₂Nanocomposite material in N₂And linear scan curves in Ar (LSV curves). As can be seen from FIG. 4, at the same potential, N₂The current density of (a) is significantly higher than that of Ar, demonstrating the occurrence of the nitrogen reduction reaction.

FIG. 5 shows Bi-MoS obtained in example 2₂NH of nanocomposites at different potentials₃Yield and Faraday efficiency plot, where the curve is the Faraday efficiency of the ammonia synthesis and the histogram is NH₃Yield. As can be seen from FIG. 5, the Bi-MoS of the present invention₂The nano composite material has good electro-catalysis ammonia synthesis performance and excellent selectivity.

Test example 3

The samples of example 2 and comparative examples 1-3 were tested for NH at the same potential-0.3V vs. RHE, according to the method of test example 2₃Yield and faraday efficiency, as shown in figure 6. Wherein the curve is the Faraday efficiency of the synthetic ammonia and the histogram is NH₃Yield.

As can be seen from FIG. 6, the Bi-MoS of the present invention₂The nano composite material has good electro-catalysis ammonia synthesis performance and excellent selectivity. Fe. Co doping element and MoS₂The performance of the electrocatalytic synthesis of ammonia cannot be improved by compounding, which shows that the selection of doping elements is important, and the doping of the Bi element plays an important role in improving the performance of the electrocatalytic synthesis of ammonia. At the same time, the carrier MoS of the composite material₂It is also important to improve the performance of the electrocatalytic synthesis of ammonia, and a material with good performance of the electrocatalytic synthesis of ammonia cannot be obtained if the carrier is not suitable, for example, carbon is used as the carrier.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention will still fall within the protection scope of the technical solution of the present invention.

Claims

1.Bi-MoS₂Use of nanocomposites, said Bi-MoS, in the electrocatalytic synthesis of ammonia₂The nano composite material takes molybdenum disulfide as a substrate, and the bismuth nanocrystals are compounded on the molybdenum disulfide substrate; the ammonia yield of the composite material can reach 15 mu g h^-1 mg^-1 _catUsing 0.5M K pH =4₂SO₄Electrolyte, wherein the Faraday efficiency of the composite material can reach 25%;

the Bi-MoS₂The nano composite material is prepared by the following method:

mixing MoS₂Dispersing in anhydrous glycol, and performing ultrasonic treatment; adding ethylene glycol solution and bismuth nitrate pentahydrate, stirring and then carrying out ultrasonic treatment to obtain mixed solution; carrying out hydrothermal reaction on the mixed solution, centrifuging, washing and drying the obtained product to obtain Bi-MoS₂A nanocomposite; the temperature of the hydrothermal reaction is 160-200 ℃, and the time of the hydrothermal reaction is 12-16 h;

mixing MoS₂In the process of dispersing in anhydrous glycol, the ratio of the mass amount of the molybdenum disulfide to the volume amount of the glycol is 5-15 mg: 5-15 ml;

in the process of adding the ethylene glycol solution and the bismuth nitrate pentahydrate, the volume dosage of the ethylene glycol and the molar dosage of the bismuth nitrate pentahydrate are 5-15 ml: 1 to 2 mmol.

2. The Bi-MoS of claim 1₂Use of a nanocomposite material for the electrocatalytic synthesis of ammonia, characterized in that MoS is added₂Dispersing in the anhydrous glycol process, wherein the ultrasonic treatment time is 1-3 h.

3. The Bi-MoS of claim 1₂The application of the nano composite material in electro-catalysis synthesis of ammonia is characterized in that in the process of adding the ethylene glycol solution and the bismuth nitrate pentahydrate, the stirring time is 8-12 hours, and the ultrasonic time is 5-15 min.

4. According to claimThe Bi-MoS of claim 1₂Use of a nanocomposite material for the electrocatalytic synthesis of ammonia, characterized in that said MoS is a catalyst₂The preparation method comprises the following steps:

5. The Bi-MoS of claim 4₂The application of the nano composite material in the electrocatalytic synthesis of ammonia is characterized in that the molar ratio of sodium molybdate dihydrate to thiourea is 1: (2-8), the ratio of the molar amount of the sodium molybdate dihydrate to the volume amount of the deionized water is 1 mol: 25-50 ml.

6. The Bi-MoS of claim 4₂Use of nanocomposites in the electrocatalytic synthesis of ammonia, characterized by MoS₂In the preparation process, the stirring time is 0.2-0.6 h, the heating reaction temperature is 180-220 ℃, and the heating reaction time is 12-24 h.