CN114671472B

CN114671472B - Preparation method of nickel sulfide nano particles for preparing formic acid by electrocatalytic reaction

Info

Publication number: CN114671472B
Application number: CN202210351888.8A
Authority: CN
Inventors: 李军山; 田晰; 李露明
Original assignee: Chengdu University
Current assignee: Chengdu University
Priority date: 2022-04-02
Filing date: 2022-04-02
Publication date: 2024-03-01
Anticipated expiration: 2042-04-02
Also published as: CN114671472A

Abstract

The invention provides a preparation method of nickel sulfide nano particles for preparing formic acid by electrocatalytic reaction, which comprises the following steps: (1) preparing nickel-sulfur slurry: mixing a nickel simple substance and sulfur powder in a proportion of 1: adding 1 molar ratio into a container, and then sequentially adding ethylenediamine and ethanedithiol into the container to obtain a mixed solution; (2) solvent evaporation: filtering insoluble particles in the mixed solution obtained in the step (1) to obtain slurry; preheating a three-neck flask, and adding the slurry; then, the three-neck flask is insulated to obtain dry powder; grinding the dry powder into fine powder; (3) powder annealing: annealing the fine powder collected in the step (2) under inert gas. The nickel sulfide nano particles prepared by the method solve the technical problems of low yield and low Faraday effect of formic acid prepared by using nickel-based non-noble metal as an electrocatalyst.

Description

Preparation method of nickel sulfide nano particles for preparing formic acid by electrocatalytic reaction

Technical Field

The invention belongs to the field of new energy materials, and particularly relates to a preparation method of nickel sulfide nano particles for preparing formic acid by electrocatalytic reaction.

Background

At present, the world economy mainly depends on non-renewable petroleum resources to operate, and carbon-based compounds related to the world are the most important chemical products in the world, but part of metabolites of the world also cause serious pollution to the ecological environment. The sustainable efficient use, conversion and storage of other renewable energy sources rich in carbon is therefore one of the effective alternatives. Among them, the use of electrocatalytic conversion of biomass-derived chemicals opens up the way for achieving this goal. In this global industrial transformation, as one of carbon recycling economy, C1 small organic molecules represented by formic acid, methanol, etc. play a variety of important roles including raw materials, intermediates, and platform compounds.

Formic acid is colorless and has a pungent odor, is very acidic and corrosive, and can stimulate skin foaming. Formic acid is used in the rubber, medical, dye, leather industry. Meanwhile, formic acid is also an organic chemical raw material and is also used as a disinfectant and a preservative. In nature, formic acid is present in secretions of bees, certain ants and caterpillars. In conventional industrial processes, some formic acid is produced as a by-product during the preparation of other chemicals, especially acetic acid, however such preparations are far from meeting the current demand for formic acid.

In industry, formic acid is generally prepared at high temperature and pressure. Under the action of strong alkali, methanol and carbon monoxide react to generate methyl formate:

CH ₃ OH+CO→HCOOCH ₃

and secondly, the base used is sodium methoxide, and the methyl formate is hydrolyzed to obtain formic acid.

HCOOCH ₃ +H ₂ O→HCOOH+CH ₃ OH

The hydrolysis of methyl formate requires a large amount of water to ensure that the reaction proceeds smoothly. In industrial production, the reaction is carried out in a liquid and pressurized state, with typical reaction conditions being 80 degrees celsius and 40 atmospheres.

In addition, some manufacturers use an indirect hydrolysis route, i.e., methyl formate is reacted with ammonia to produce formamide, which is then hydrolyzed with sulfuric acid to produce formic acid:

HCOOCH ₃ +NH ₃ →HCONH ₂ +CH ₃ OH

2HCONH ₂ +2H ₂ O+H ₂ SO ₄ →2HCOOH+(NH ₄ ) ₂ SO ₄

this technique has its own drawbacks, especially in the treatment of the by-product ammonium sulphate. Some manufacturers have recently developed an energy efficient process that extracts formic acid from large amounts of aqueous solutions that are directly hydrolyzed. In one of these processes (used by basf), formic acid is obtained by wet extraction under the action of an organic base.

In laboratory preparations, formic acid can be obtained by heating oxalic acid in anhydrous glycerol and then steam distillation. Another preparation method is the hydrolysis of isopropyl nitrile under the action of hydrochloric acid.

C ₂ H ₅ NC+2H ₂ O→C ₂ H ₅ NH ₂ +HCOOH

The preparation of isopropyl nitrile is obtained from the reaction of ethylamine and chloroform. Notably, the excessively unpleasant odor of the isopropanitrile necessitates that this reaction be carried out in a fume hood.

In general, the above industrial and experimental preparation of formic acid generally requires high temperature and high pressure or generates toxic and harmful gases, and thus, there is an urgent need for a new method for preparing formic acid, particularly for preparing formic acid at normal temperature and pressure with high efficiency. Based on the electrochemical advantages, intermittent characteristics of sustainable energy sources, such as solar energy, wind energy and the like, are utilized to the maximum extent, and the surplus energy sources are converted into common chemicals, so that not only can the dependence on fossil resources be reduced, but also the industrial cost and reaction conditions of corresponding carbon-based chemical products are reduced, and the method is one of the priority roads for sustainable development of future energy sources.

Nickel sulfide NiS has high metal conductivity, good electrocatalytic activity and good chemical stability, and is a promising electrocatalyst. CN113802139a discloses a nickel sulfide base electrocatalytic material with a core-shell structure and a preparation method thereof: uniformly dispersing nickel chloride hexahydrate, urea and ammonium fluoride in water to obtain a solution A, ultrasonically cleaning foam nickel, and drying to obtain treated foam nickel; reacting the treated foam nickel with the solution A, naturally cooling to obtain reacted foam nickel, cleaning the reacted foam nickel, and drying to obtain a precursor; uniformly dispersing ammonium metavanadate and thioacetamide in water to obtain a solution B; the precursor reacts with the solution B, and after the reaction is finished, the Ni coated with the amorphous VOx is obtained after natural cooling ₃ S ₂ The foam nickel product is washed and dried to prepare the nickel sulfide-based electrocatalytic material with the core-shell structure. The method improves the stability of nickel sulfide as an electrocatalyst. However, there is little research on the application of non-noble metal-based catalysts to electrocatalytic methanol, and the present invention is intended to achieve efficient electrocatalytic methanol conversion to formic acid based on inexpensive materials.

Disclosure of Invention

The invention aims to provide a preparation method of nickel sulfide nano particles for preparing formic acid by electro-catalysis, which aims to solve the technical problems of low yield and low Faraday efficiency of preparing formic acid by taking nickel-based non-noble metal as an electro-catalyst.

In order to solve the technical problems, the specific technical scheme of the preparation method of the nickel sulfide nano-particles for preparing formic acid by electrocatalytic reaction is as follows:

a method for preparing nickel sulfide nano-particles for electrocatalytically preparing formic acid, which comprises the following steps:

(1) Preparing nickel-sulfur slurry: mixing a nickel simple substance and sulfur powder in a proportion of 1: weighing the mixture according to a molar ratio of 1, adding the mixture into a container, and sequentially adding ethylenediamine and ethanedithiol into the container to obtain a mixed solution; stirring the mixed solution;

(2) Solvent evaporation: filtering insoluble particles in the mixed solution obtained in the step (1) by using polytetrafluoroethylene to obtain slurry; preheating a three-neck flask, and adding the slurry; argon is introduced into the three-necked flask from one neck, and the other neck is connected with vacuum so as to quickly remove steam in the slurry; placing a safety flask between the vacuum and the other neck to collect vapors emanating from the slurry; then, the three-neck flask is insulated to obtain dry powder; grinding the dry powder into fine powder, and performing subsequent annealing treatment;

(3) Powder annealing: and (3) annealing the fine powder collected in the step (2) under inert gas to obtain nickel sulfide nano particles.

Further, in the step (1), the volume ratio of ethylenediamine to ethanedithiol is 3.3:0.3.

further, in the step (1), the stirring conditions are as follows: stirring is carried out at 750 rpm for 24 hours at room temperature.

Further, in the step (2), the polytetrafluoroethylene has a diameter of 0.45 μm.

Further, in the step (2), the temperature of the three-necked flask preheating was 250 ℃.

Further, in the step (2), the three-necked flask was kept warm for 10 minutes.

Further, in the step (3), the annealing condition is: placing the fine powder in a tubular furnace under the argon atmosphere at 300 ℃ for 1 hour, heating at the speed of 3 ℃/min, and then preserving the temperature for 30 minutes at 400 ℃ to obtain the nickel sulfide nano-particles.

The preparation method of the nickel sulfide nano-particles for preparing formic acid by electrocatalytic reaction has the following advantages: the electrocatalytic performance is far higher than the reference value of a single metal nickel electrode, so that the yield of formic acid is greatly improved; the simple material synthesis method and the synthesis method of the formic acid with low cost at normal temperature and normal pressure have wide prospects in sustainable energy and environmental application.

Drawings

Fig. 1 is a diagram of the present invention: (a) nickel sulfide nanoparticle X-ray diffraction pattern; (b) TEM images of nickel sulfide nanoparticles and their size distribution; (c) an X-ray diffraction pattern of elemental Ni nanoparticles; (d) TEM images and size distributions of elemental Ni nanoparticles;

FIG. 2 is a graph showing the morphology characterization of nickel sulfide nanoparticles of the present invention: (a) High-power electron microscope pictures and element distribution of nickel sulfide nano particles; (b) Diffraction patterns and schematic diagrams of crystal structures of nickel sulfide nano particles; (c) SEM images of nickel sulfide nanoparticles; (d) a profile of nickel sulfide nanoparticle EDS elements;

FIG. 3 is a graph of voltammetric cycle curves versus the nickel sulfide nanoparticle-based electrode of the present invention (a) Ni elemental nanoparticle-based electrode (b) in the absence (dashed line) or presence of 1 mole per liter of methanol (solid line) in 1 mole per liter of KOH lye; and (3) injection: the current density (J) is calculated from the measured current (i) divided by the geometric area of the glassy carbon electrode (0.196 square cm);

FIG. 4 shows the non-Faraday range electrochemical activity of the nickel sulfide nanoparticle-based electrode (a-b) and the Ni elemental nanoparticle-based electrode (c-d) of the present invention in 1M KOH: (a, c) is between 1 and 100mV s ^-1 CV curve in the potential range of 0.9-1.0V at different scanning rates; (b, d) positive and negative scans at a current of 0.95V versus scan rate.

FIG. 5 shows the electrochemical activity of the nickel sulfide nanoparticle-based electrode (a-c) and the Ni elemental nanoparticle-based electrode (d-f) of the present invention in the Faraday (0.9-1.6V) range of 1 mol/liter KOH: (a, d) CV curves at different scan rates; (b, e) the oxidation-reduction peak current and the scanning rate are 10-50 mV s ^-1 Linearity betweenFitting the square root of the (c, f) redox peak current to the sweep rate at 60-100 mV s ^-1 Linear fitting between;

fig. 6 is a stability test and faraday efficiency of the nickel sulfide nanoparticle-based electrode and Ni elemental nanoparticle-based electrode of the present invention: (a) Under the additional voltage of 1.6V in a solution of 1 mol/L KOH and 1.6V in a solution of mol/L methanol, the stability of the nickel sulfide nanoparticle-based electrode and the Ni simple substance nanoparticle-based electrode is tested, and the test time is 10000 seconds; (b) Ion chromatography curve of the solution at the end of the stability test; (c) Faradaic efficiency of nickel sulfide nanoparticle-based electrodes and Ni elemental nanoparticle-based electrodes.

Detailed Description

In order to better understand the purpose, structure and function of the present invention, the preparation method of the nickel sulfide nano-particles for preparing formic acid by electrocatalytic reaction and the promotion of the electrocatalytic activity thereof are described in further detail below with reference to the accompanying drawings on the basis of comparison with the simple substance metal nickel electrocatalytic material.

Based on the method, the inventor adopts cheap metal as a raw material, and synthesizes the NiS nano material with precise control. The NiS nano-particles are divided into a total of 3 steps.

First, i) a nickel-sulfur slurry is produced. Mixing a nickel simple substance and sulfur powder in a proportion of 1:1 molar ratio (2 mmol total) was weighed into a 10 ml glass bottle and 3.3 ml ethylenediamine and 0.3 ml ethylenediamine were added sequentially to the bottle. The mixture was stirred at 750 rpm for 24 hours at room temperature. The long-time stirring ensures that the simple substance nickel and the sulfur powder are fully mixed to form uniform precursor slurry.

Second, ii) solvent evaporation. Insoluble particles were filtered with polytetrafluoroethylene having a diameter of 0.45 microns (filtering out the insufficiently dissolved large particle size nickel and sulfur powder to reuse the resulting nanoparticles free of nickel and elemental material) and left in the filter flask for use. Argon was introduced into the flask from one neck of the three-necked flask while the other neck was connected to a vacuum to rapidly remove vapors from the slurry. A safety flask containing water/ethanol was placed between the vacuum and the reaction flask to collect vapors emanating from the slurry solution. After the flask was preheated to 250 ℃, the slurry was added with a syringe, and the temperature of the three-necked flask was lowered first and then slowly raised to 250 ℃. And then the flask is kept warm for about 10 minutes to obtain dry powder, and nano particles with uniform morphology can be obtained at the temperature, so that the high-efficiency and stable electrocatalytic activity is obtained. And grinding the product into fine powder, and carrying out subsequent annealing treatment.

Finally, iii) powder annealing. Placing the collected fine powder in a tubular furnace for 1 hour under the argon atmosphere at 300 ℃, heating at the speed of 3 ℃/min, and then preserving the temperature at 400 ℃ for 30 minutes to finally obtain the nickel sulfide nano particles. Annealing under an inert atmosphere can prevent oxide formation on the one hand and can improve the crystallinity of the nano particles on the other hand.

By contrast, the inventors prepared Ni elemental nanoparticles of the same diameter using the following method: a three-necked flask was charged with a magnetic bar, 1 mmol of nickel acetylacetonate, 2.7 ml of oleylamine, 0.4 mmol of n-trioctyl phosphorus and 0.25 mmol of n-trioctyl phosphorus oxide, kept at 130℃for 30 minutes, and purged with argon. The flask was then rapidly heated to 215 ℃ and held at this temperature for 45 minutes. Subsequently, the flask was cooled to room temperature using a water bath. After adding ethanol, the black precipitate was centrifuged. To further remove the surface residual ligand, the precipitate was dispersed in a mixture containing 28 ml of acetonitrile and 0.8 ml of hydrazine hydrate and stirred for about 2 hours before testing for electrochemical performance. After centrifugation, the mixture was washed 3 times with acetonitrile. Finally, drying under vacuum for later use.

As shown in FIG. 1a, the X-ray diffraction pattern of the nickel sulfide nanoparticles shows that they have a nickel sulfide phase (JCPLS No. 01-075-0613). TEM characterization indicated that the particles obtained have an average diameter of about 12 nm (FIG. 1 b). The elementary Ni nanoparticles as a comparative reference conform to the crystalline phase of elementary Ni (FIG. 1c, JCPDS No. 03-065-0390), and the size thereof is about 12 nm (FIG. 1 d).

Fig. 2 demonstrates that the synthesized nickel sulfide nano-particles have uniform element components and excellent crystal structure, and provide possibility for serving as a high-performance catalyst. The EELS chemical composition diagram shown in fig. 2a shows a uniform distribution of Ni and S. As shown in fig. 2b, HRTEM indicates that the nanoparticles have good crystallinity,conforms to the NiS hexagonal phase (space group=P63/mmc), and has a unit cell size of SEM-EDS analysis showed a Ni to S atomic ratio of 1:1, as shown in FIG. 2c, FIG. 2 d.

Electrocatalytic experiments generally employ a three-electrode system to test its methanol oxidation properties: the glassy carbon electrode is a working electrode, the Pt wire is a counter electrode, and Hg/HgO is a reference electrode. The electrocatalyst slurry needs to be formulated before testing for electrochemical properties. A5 mg sample (nickel sulfide nano-particles as high-efficiency electrocatalytic material; ni simple substance nano-particles as comparative material) was dissolved in 1 ml water, 1 ml ethanol and 0.1 ml Nafion, and stirred ultrasonically for 1 hour. And 5 microliters of newly prepared electrocatalyst slurry is taken by a pipetting gun and is dripped on a glassy carbon electrode with the diameter of 5 millimeters to respectively obtain a Ni simple substance nano particle-based electrode and a nickel sulfide nano particle-based electrode. And after the sample is naturally dried, connecting the sample with a direct electrochemical workstation as a working electrode for testing and analysis. For comparison purposes, the applied voltage (with Hg/HgO) is converted to a reversible hydrogen electrode potential according to the following Nernst equation:

E _RHE ＝E _Hg/HgO +0.059×pH+E ^θ _Hg/HgO

wherein E is _Hg/HgO For applying voltage E ^θ _Hg/HgO Is the potential of the reference electrode (0.098V), and a pH of 1M KOH solution corresponds to the actual value (13.6 measured with a pH meter).

The method comprises the steps of adopting a Ni simple substance nano particle-based electrode and a nickel sulfide nano particle-based electrode, wherein the concentration of an electrolytic liquid is 1 mol/L KOH solution and 1 mol/L methanol solution. As shown by the broken line in fig. 3, when methanol is not added, the current density increases sharply at about 1.342V, forming an oxidation peak of NiOOH, and then at about 1.65V, the current density increases again, mainly due to the generation of oxygen. On the other hand, in the presence of 1 mol/l methanol, the current density starts to increase at about 1.311V, mainly due to methanol electricityOxidation provides an electrical current. The electrocatalytic performance of the nickel sulfide nanoparticle-based electrode was 121.2mA cm at a potential of 1.6V relative to a standard hydrogen electrode ^-2 As shown in fig. 3 a; is greatly higher than that of Ni simple substance nano particle base electrode by 56.8mA cm ^-2 As shown in fig. 3b. In general, the preparation of formic acid by oxidation of methanol can be generally divided into the following four steps: (1) NiOOH active material generation; (2) adsorption of methanol; (3) dehydrogenation of methanol to formaldehyde; (4) further oxidation of formaldehyde to formic acid:

(1)OH ^- +Ni(OH) ₂ →NiOOH+H ₂ O+e-

(2)CH ₃ OH _sol. →CH ₃ OH _ads.

(3)CH ₃ OH _ads. +NiOOH→C*H ₂ OH+Ni(OH) ₂

(4)C*H ₂ OH+3NiOOH+OH ^- →CHOO ^- +3Ni(OH) ₂

the overall reaction occurring at the positive electrode is as follows:

CH ₃ OH+5OH ^- →HCOO ^- +4H ₂ O+4e ^-

meanwhile, hydrogen evolution reaction is carried out in the negative electrode reaction:

2H ₂ O+2e ^- →2OH ^- +H ₂

improving intrinsic parameters of the single metal material, such as: electrochemically active area (electrochemically active surface areas, ECSA), active site coverage area (surface coverage of redox species, Γ ^* ) And its diffusion coefficient (diffusion coefficient, D) etc. can improve the properties of the electrocatalytic material. On one hand, the nano-size range of the material can greatly increase the specific surface, so that the catalytic active sites are increased; on the other hand, the hybridization of single metal can effectively change the electronic structure, thereby improving the intrinsic characteristics of the electrocatalyst. The invention will illustrate the enhancement of the electrocatalytic activity of nickel sulfide nanoparticles in terms of their electrochemical active area (ECSA), active site coverage area and diffusion coefficient, respectively.

Electrochemically active area (ECSA):

under alkaline conditionsThe formation of NiOOH active species plays a decisive role in the electrochemical performance of methanol oxidation, and the intrinsic parameters associated with this are: electrochemically active surface area (ECSA), active site coverage area of redox species, diffusion coefficient, etc. First, CV curves and electrochemical double layer capacitance (C) at different scan rates over the non-Faraday potential range 0.9-1.0V vs. RHE (FIG. 4 a) _dl ) The electrochemically active surface area (ECSA) can be estimated as shown in fig. 4 b. The capacitance current (i) is plotted between the current at 0.95V and the scan rate (V) to obtain a slope equal to C _dl Is shown (fig. 4 b).

ECSA＝C _dl /C _s

As shown in FIG. 4C and FIG. 4d, by the formula C _dl Divided by specific capacitance (C _s 0.04) to calculate the nickel sulfide ECSA to be 6.4cm ² 5.5cm higher than nickel ² 。

Active site coverage area:

at 10-100 mV s ^-1 The inventors compared the CV curves of the nickel sulfide nanoparticle-based electrode and the Ni elemental nanoparticle-based electrode in the faraday range. As shown in fig. 5a and 5d, as the scanning rate increases, the positions of the positive electrode peaks of the nickel sulfide nanoparticle-based electrode and the Ni elemental nanoparticle-based electrode move in the direction in which the potential is high, and the positions of the negative electrode peaks move in the direction in which the potential is low. Its positive and negative peak current (I) _pc ,I _pa ) Both increase linearly with increasing scanning speed (fig. 5b and 5 e). To obtain accurate active site coverage, peak current (I _p ) Taking the peak current of the positive and negative poles (I) _pc ,I _pa ) Average value of (2). From the average slope of the positive and negative peak currents with the scan speed, the active site coverage area (Γ) can be calculated by the following formula ^* )：

Wherein n, F, R, T and A are respectively the number of transferred electrons (n=1 in this case), faraday constant (96845C mol) ^-1 ) Constant of gas(8.314J K ^-1 mol ^-1 ) Temperature and geometric surface area of the glassy carbon electrode (0.196 cm ² ). From the above equation, it can be calculated that the active site coverage area (Γ) of the nickel sulfide nanoparticle-based electrode (FIG. 5 b) ^* ) 1.48×10 ^-6 mol cm ^-2 1.61×10 higher than the Ni elemental nanoparticle based electrode (FIG. 5 e) ^-7 mol cm ^-2 An order of magnitude.

Diffusion coefficient:

electrochemical properties are related not only to the NiOOH active site coverage area, but also to its diffusion coefficient, and diffusion of the active species is generally considered a critical process limiting the reaction rate. As shown in fig. 5c and 5f, the peak currents (I _pc ,I _pa ) A straight line can be fitted to the square root of the scan rate, and the diffusion coefficient can be calculated by the following equation:

I _p ＝2.69×10 ⁵ n ^3/2 AD ^1/2 Cv ^1/2

wherein n, a, C and v are the number of transferred electrons (in this case n=1), and the geometric surface area of the glassy carbon electrode (0.196 cm ² ) Proton concentration and scan rate. Wherein, according to the related literature, C is a proton concentration estimated to be 3.97g cm ^-3 . To obtain a precise diffusion coefficient, the peak current (I _p ) Taking the peak current of the positive and negative poles (I) _pc ,I _pa ) Average value of (2). The rate limiting diffusion coefficient of the Ni elemental nano particle based electrode can be calculated by using the equation ^-7 cm ² s ^-1 (FIG. 5 f), slightly below the rate limiting diffusion coefficient of the nickel sulfide nanoparticle-based electrode of 3.78X10 ^-7 cm ² s ^-1 (FIG. 5 c).

To test the electrochemical stability of the catalyst, the inventors performed a long-period chronoamperometric stability test of 10000 seconds in 1 mol/l KOH solution and 1 mol/l methanol. As can be seen from fig. 6a, the current density of the two electrodes decreased rapidly in the first few minutes and then became stable, and after 10000s of reaction, the current density of methanol oxidation on the nickel sulfide nanoparticle-based electrode and the Ni elemental nanoparticle-based electrode82.9 and 45.1mA cm respectively ^-2 。

To calculate the amount of formic acid produced by oxidation of methanol and the faraday efficiency, the solution is usually calibrated. First, 0.5 ml of the solution after the stability test was diluted into 8 ml of purified water, and then tested by ion chromatography. As shown in fig. 6b, the upward peak at 4.8 minutes corresponds to formic acid. Under the test condition of 10000 seconds and 1.6V, 0.45 millimole of formic acid is electrochemically generated on the nickel sulfide nano particle-based electrode, which is higher than the generation amount of 0.27 millimole of formic acid on the Ni simple substance nano particle-based electrode. In addition, the faraday efficiency of methanol oxidation under this condition can be calculated using the faraday efficiency formula:

wherein n is the electron transfer number (4 electron transfers from methanol to formic acid), F is Faraday constant (96485C mol) ^-1 ). The faradaic efficiency of the nickel sulfide nanoparticle-based electrode was calculated to be 98.1% and 96.6%, respectively, higher than that of the Ni elemental nanoparticle-based electrode for oxidation of methanol to formic acid, as shown in fig. 6 c.

In summary, the inventors provide a method for preparing nickel sulfide nanoparticles for electrocatalytically preparing formic acid. The electrocatalytic performance of the catalyst on methanol oxidation is studied in an alkaline medium, and the test result is far higher than the reference value of the Ni simple substance nano particle-based electrode. The introduction of sulfur does not improve Faraday efficiency of formic acid, but greatly improves the production of chemicals, and the yield of the nickel sulfide nanoparticle-based electrode formic acid is 0.17 mmol/h, which is almost simple substance NiNan (nanometer)Twice the yield of the nanoparticle-based electrode.

It will be understood that the invention has been described in terms of several embodiments, and that various changes and equivalents may be made to these features and embodiments by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method for preparing nickel sulfide nano-particles for electrocatalytically preparing formic acid, which is characterized by comprising the following steps:

(3) Powder annealing: annealing the fine powder collected in the step (2) under inert gas to obtain nickel sulfide nano particles;

in the step (1), the volume ratio of the ethylenediamine to the ethanedithiol is 3.3:0.3; the stirring conditions are as follows: stirring at 750 rpm for 24 hours at room temperature; in the step (2), the diameter of the polytetrafluoroethylene is 0.45 micrometers; the preheating temperature of the three-neck flask is 250 ℃; the temperature keeping time of the three-neck flask is 10 minutes; in the step (3), the annealing conditions are as follows: the fine powder was placed in a tubular furnace under an argon atmosphere at 300℃for 1 hour, heated at a rate of 3℃/min, and then incubated at 400℃for 30 minutes to obtain post-nickel sulfide nanoparticles.