CN115161667A - Preparation method of electrocatalytic material alkanethiol-VS2 for ENRR - Google Patents

Abstract

A preparation method of an electrocatalytic material alkanethiol-VS ₂ for ENRR belongs to the field of electrocatalytic nitrogen fixation. The mixed hydrothermal method includes vanadium disulfide raw material, vanadium disulfide material is loaded on carbon paper, and the loaded carbon paper is soaked in alkyl mercaptan to synthesize working electrode. The invention is mainly used for preparing alkyl mercaptan-VS _{2 electrocatalytic nitrogen fixation material, and solves the problem of poor selectivity of VS 2 catalyst} for ENRR. Among them, the vanadium disulfide VS ₂ material obtained hydrothermally with ammonium metavanadate as the vanadium source and thioacetamide as the sulfur source was coated on carbon paper as a working electrode to participate in ENRR, and there was a serious competitive hydrogen evolution in the process. Compared with the reaction, in the present invention, the carbon paper coated with the above synthesized VS ₂ material is soaked in alkyl thiol to obtain a working electrode modified by surface alkyl thiol, and the number of catalytic surface protons is reduced by introducing hydrophobic alkyl thiol. In turn, the competitive hydrogen evolution reaction is inhibited, and the purpose of improving the selectivity of ENRR is achieved.

Description

Preparation method of electrocatalytic material alkanethiol-VS2 for ENRR

technical field

The invention belongs to the field of electrocatalytic reduction of nitrogen to produce ammonia, and specifically discloses a preparation method of an electrocatalytic material alkanethiol-VS ₂ for ENRR.

Background technique

Ammonia (NH ₃ ), as a commodity raw material, fertilizer raw material and chemical precursor, is an essential substance to maintain human life and global economic development, and is also a new type of effective hydrogen storage medium and non-carbon emission fuel. However, current industrial methods for ammonia production still rely heavily on the traditional energy-intensive Haber-Bosch process (HBP). Electrochemical nitrogen reduction reaction (ENRR) has been regarded as the most promising alternative to Haber in recent years due to its mild operating conditions at room temperature and pressure, coupled with green energy, no CO2 emissions, and the use of abundant water instead of high-purity hydrogen. - Method of the Bosch process. Unfortunately, its practical application is still challenging, mainly because the strong dinitrogen bond is difficult to break and a competitive hydrogen reduction reaction (HER) occurs simultaneously, resulting in low _NH3 yield and efficiency. In view of the above problems, it is urgent to develop novel electrocatalysts with high ENRR catalytic performance.

Vanadium disulfide (VS ₂ ) materials have been widely used in the field of ENRR in recent years due to their unique physicochemical properties and electronic configuration. However, in the conventional VS2 electrocatalytic nitrogen reduction reaction, the _ENRR selectivity is poor and the FE ratio is low due to its abundant sulfur edges providing abundant hydrogen evolution reaction sites. In order to solve this problem, a surface alkylthiol-modified vanadium disulfide (alkylthiol-VS ₂ ) was designed as a catalytic material. The introduction of hydrophobic alkylthiol can reduce the number of protons at the catalytic interface and effectively inhibit the competition. HER reaction, showing excellent catalytic selectivity in ENRR.

SUMMARY OF THE INVENTION

Aiming at the problem of poor selectivity of existing catalysts, the present invention aims to prepare a method for preparing a surface-modified catalyst alkanethiol-VS ₂ which can improve the selectivity of the catalyst, which can improve the catalytic selectivity of ENRR during the reaction process, and further Improve FE and effectively inhibit the competitive HER reaction.

In order to solve the above technical problems, the present invention provides an alkylthiol-modified vanadium disulfide (alkylthiol-VS ₂ ) material for electrocatalytic nitrogen reduction and a preparation method thereof, including ammonium metavanadate and thiol The raw materials of acetamide are mechanically stirred and mixed in ultrapure water, the mixed solution is microwave hydrothermal, the black solid obtained by hydrothermal suction filtration washing is vacuum dried to obtain VS ₂ black powder material; a certain amount of VS ₂ powder is taken and dissolved in ethanol-water - Ultrasound in Nafion solution to obtain a uniform oily solution, take a certain amount of the above solution and evenly coat it on carbon paper to obtain a carbon paper material supported by VS ₂ ; finally, soak the above-mentioned dried carbon paper in argon-saturated alkyl sulfide In alcohol-ethanol solution, the surface alkylthiol modified vanadium disulfide (alkylthiol-VS ₂ ) electrode material was obtained.

Further, the molar ratio of the ammonium metavanadate and the thioacetamide is 1:3.

Further, the mechanical stirring and mixing are realized by magnetic stirring, and the specific stirring time is 1 h.

Further, the specific process of the microwave hydrothermal heating is as follows: heating from room temperature to 120° C. in 10 minutes, and keeping at this temperature for 8 minutes; then heating to 150° C. for 10 minutes, and keeping at this temperature for 8 minutes; then heating to 180° C. for 10 minutes , and kept at this temperature for 120min; finally cooled to room temperature naturally.

Further, the solvents used in the suction filtration and washing are dehydrated ethanol and ultrapure water, respectively, and the washing times are 3 times.

Further, the specific conditions of the vacuum drying are: -30MPa, 60°C and 24h.

Further, each 5mg VS ₂ powder corresponds to 800-1200 μl of ethanol-water-Nafion solution; wherein the volume ratio of ethanol, water and Nafion solution is 654:326:20, and the Nafion solution is a perfluorosulfonic acid type polymer solution, which can be used as a catalyst The coating or carrier reduces the transport resistance of the substance and the resistance of the electrode.

Further, the ultrasonic time is 1h to obtain a uniform oily solution.

Further, each 1 cm ² of carbon paper size corresponds to 15-25 μl of the oily solution.

Further, the volume ratio of alkyl mercaptan to ethanol in the alkyl mercaptan-ethanol is 2:15-25.

Further, the soaking time is 5-20 min, and the vanadium disulfide (alkylthiol-VS ₂ ) modified with the surface alkyl thiol is taken out.

Further, the alkylthiol is a C2-C12 alkylthiol.

The invention effectively suppresses the competitive hydrogen evolution reaction while ensuring that the prepared material has a certain catalytic activity, improves the reaction selectivity, and the obtained material has a uniform microscopic appearance. The above features contribute to the in-depth study of the ENRR process.

Description of drawings

Figure 1 is a schematic diagram of the microscopic morphology of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ for ENRR according to the present invention;

2 is a schematic diagram showing the comparison of the water contact angle test of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ for ENRR according to the present invention;

3 is a schematic diagram of the electrolysis device of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ used for ENRR according to the present invention;

FIG. 4 is a schematic diagram of the chronoamperometry of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ used for ENRR according to the present invention;

5 is a schematic diagram of the ultraviolet-visible light spectrum of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ used for ENRR according to the present invention;

6 is a schematic diagram showing the comparison of the ammonia yields of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ for ENRR according to the present invention;

FIG. 7 is a schematic diagram showing the comparison of Faradaic efficiencies of the electrocatalytic materials alkanethiol-VS ₂ and VS ₂ for ENRR according to the present invention.

Detailed ways

The following is a further detailed description through specific embodiments, but the present invention is not limited to the following examples.

Referring to Figure 1, an electrocatalytic material for ENRR, alkanethiol-VS ₂ , is mainly composed of alkanethiol materials supported on carbon paper coated with VS ₂ catalyst.

Preparation method: Mix 5mmol of ammonium metavanadate, 15mmol of thioacetamide and 40mL of ultrapure water, stir magnetically for 1h to obtain a black turbid solution. The above solution was transferred to a microwave hydrothermal reactor, and the hydrothermal synthesis process was as follows: heating from room temperature to 120°C in 10min, and keeping the temperature at this temperature for 8min; then heating to 150°C in 10min, and keeping the temperature at this temperature for 8min; then Heated to 180°C for 10min, and kept at this temperature for 120min; finally cooled to room temperature naturally. After cooling to room temperature, the obtained black solution was vacuum filtered, washed with absolute ethanol and ultrapure water for 3 times, and finally vacuum-dried for 12 h to obtain black solid powder VS ₂ material; 5 mg of the VS ₂ powder prepared by the above method was dissolved in 1000 μl of ethanol-water-Nafion solution with a ratio of 654:326:20 was sonicated for 1 h to obtain a uniform oily solution, and 20 μl of the above solution was uniformly coated along the broad side with 1*1cm ² of carbon with a total size of 2*1cm ² On the paper, the VS ₂ material supported by carbon paper was obtained; finally, the above-mentioned carbon paper after drying was soaked in 22ml of argon-saturated alkyl mercaptan and ethanol ratio of 2:20 in the alkyl mercaptan-ethanol solution of 2:20 for 10 minutes. The alkyl mercaptans are n-butane mercaptan, n-octane mercaptan and n-dodecane mercaptan with different carbon chain lengths, respectively, and the surface alkyl mercaptan modified vanadium disulfide (alkyl mercaptan-VS ₂ ) electrode is obtained Material.

In this example, the electrode was characterized and analyzed by scanning electron microscope. It can be seen from Figure 1 that the material is mainly composed of alkylthiol supported on carbon paper coated with VS ₂ catalyst.

Figure 2 is a schematic diagram of the comparison of the water contact angle test of the material of the present invention. It can be seen from the figure that the water contact angle of the material of the present invention is greater than 90°, which is a hydrophobic material; while the water contact angle of VS ₂ is less than 90°, which is a hydrophilic material. The above test results prove the successful synthesis of the alkanethiol-VS ₂ material and the better hydrophobicity of the material of the present invention, thereby effectively inhibiting the competitive hydrogen evolution reaction.

3 is a schematic diagram of an electrolysis device of the material of the present invention; the working electrode is the electrocatalytic material alkylthiol-VS2 of the present invention, the counter electrode is a silver/silver chloride reference electrode, and a double electrolysis chamber is used, and the specific parameters are: 0.1M After the Na2SO4 electrolyte was purified by N2 for 30min, the N2 reduction experiment was carried out. Electrochemical reduction of _N2 was carried out in _{N2 -} saturated 0.1 M _Na2SO4 solution. After electrolysis at a controlled potential (-0.10 to -0.30V vs. RHE) for a period of time, the electrolyte in the cathode cell was collected for color development, its absorbance was measured with a UV spectrophotometer, and its ammonia yield and Faradaic efficiency (FE) were calculated. . Its calculation formula is:

The _formula for calculating the generation rate of NH is as follows:

为产氨量，单位为

为电解液中NH₃的浓度，单位为μg mL^-1；V为电解液体积，单位为mL；t为电解时间，单位为h；m_cat为电极材料的质量，单位为mg。

is the ammonia production, the unit is

is the concentration of NH ₃ in the electrolyte, the unit is μg mL ^-1 ; V is the volume of the electrolyte, the unit is mL; t is the electrolysis time, the unit is h; m _cat is the mass of the electrode material, the unit is mg.

The formula for calculating FE is as follows:

FE is the Faraday efficiency, the unit is %; F is the Faraday constant, its value is 96500C mol ^-1 ; Q is the total charge consumption in the electrolysis process, the unit is C.

Figure 4 is a schematic diagram of the chronoamperometry of the material of the present invention. The specific parameters are: the potential settings are -0.10, -0.15, -0.20, -0.25, -0.30V vs. RHE; the point interval is 0.05s; the running time is 7200s; the sensitivity is 0.1A/V. It can be seen from Figure 5 that at different potentials, the corresponding currents fluctuate within a small range, proving that the material has a certain catalytic stability.

Figure 5 is a schematic diagram of the ultraviolet-visible light spectrum of the material of the present invention. It can be seen from the figure that under the optimal reduction potential, the material of the present invention has a higher NH ₃ absorption peak at a wavelength of 655 nm, which proves that the material of the present invention has better electrocatalytic ammonia production performance.

Figure 6 is a schematic diagram of ammonia production of the material of the present invention. It can be seen from the figure that under the same reduction potential, the ammonia production of the materials of the present invention is all higher than that of VS ₂ , and the highest is 58.1 μg h ^-1 mg _cat ^-1 , while the highest ammonia production of VS ₂ is only 58.1 μg h -1 mg cat -1 . 20.6μgh ^-1 mg _cat ^-1 . It is proved that the material of the present invention has more excellent electrocatalytic ammonia production performance.

Figure 7 is a schematic diagram of the Faradaic efficiency of the material of the present invention. It can be seen from the figure that under the same reduction potential, the FE value of the material of the present invention is all higher than that of VS ₂ , and the highest FE value reaches 34.5%, while the highest FE value of VS ₂ is only 8.7%. It is proved that the material of the present invention has higher selectivity.

The above descriptions are only examples of the present invention, and common knowledge such as well-known specific structures and characteristics in the solution are not described too much here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation of the present invention. effect and the applicability of the patent.

Claims (10)

1. a preparation method for the alkanethiol _- VS material for electrocatalytic reduction of nitrogen, is characterized in that, comprises that ammonium metavanadate and thioacetamide raw materials are mechanically stirred and mixed in ultrapure water, and the mixed The solution is microwaved and hydrothermally heated, and the black solid obtained by hydrothermal suction is filtered, washed, and vacuum-dried to obtain VS ₂ black powder material; a certain amount of VS ₂ powder is dissolved in ethanol-water-Nafion solution and ultrasonicated to obtain a uniform oily solution, and a certain amount of the above-mentioned The solution was evenly coated on carbon paper to obtain VS ₂ loaded carbon paper material; finally, the above-mentioned dried carbon paper was immersed in an argon-saturated alkylthiol-ethanol solution to obtain a surface alkylthiol-modified carbon paper. The vanadium sulfide electrode material is alkanethiol-VS ₂ material. 2. according to the described method of claim 1, it is characterized in that, the mol ratio of described ammonium metavanadate, thioacetamide is 1:3; The concrete process of described microwave hydrothermal is: 10min is heated from room temperature to 120 ℃, and kept at this temperature for 8 min; then heated to 150 ℃ for 10 min, and kept at this temperature for 8 min; then heated to 180 ℃ for 10 min, and kept at this temperature for 120 min; finally cooled to room temperature naturally. 3. according to the method described in claim 1, it is characterized in that, the solvent that described suction filtration washing is used is dehydrated alcohol and ultrapure water respectively, and the number of times of washing is 3 times; The concrete condition of described vacuum drying is: -30MPa, 60°C and 24h. 4. according to the described method of claim 1, it is characterized in that, every 5mg VS ₂ powder corresponds to 800-1200 μl ethanol-water-Nafion solution; Wherein ethanol, water, Nafion solution volume ratio are 654:326:20, and Nafion solution is The perfluorosulfonic acid type polymer solution can be used as a coating or carrier for catalysts, reducing the transmission resistance of substances and the resistance of electrodes. 5. The method according to claim 1, wherein the size of each 1 cm ² of carbon paper corresponds to 15-25 μl of the oily solution. 6. according to the method for claim 1, it is characterized in that, in described alkyl mercaptan-ethanol, alkyl mercaptan and ethanol volume ratio are 2:15-25. 7. method according to claim 1 is characterized in that, described soaking time is 5-20min, take out and obtain the vanadium disulfide modified by surface alkyl mercaptan, and described alkyl mercaptan is C2-C12 alkyl sulfide alcohol. 8. The alkylthiol-VS ₂ material prepared according to the method of any one of claims 1-7. 9. The application of the alkanethiol-VS ₂ material prepared by the method according to any one of claims 1-7, as an electrode for electrocatalytic reduction of nitrogen to prepare ammonia. 10. The method according to claim 9, wherein the working electrode is an electrocatalytic material alkanethiol-VS2, the counter electrode is a silver/silver chloride reference electrode, and a double electrolysis chamber is used, and the specific parameters are: 0.1 The _N2 reduction experiment was carried out after the _N2 purification in M _Na2SO4 electrolyte for 30 min _; the _N2 electrochemical reduction was carried out in the _N2 saturated 0.1 M _Na2SO4 solution _; at the control potential -0.10 to - 0.30V vs. RHE.

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