Cobalt phosphide nano-catalyst as well as preparation method and application thereof

Abstract

The invention provides a cobalt phosphide nano-catalyst as well as a preparation method and application thereof. The cobalt phosphide nano-catalyst is prepared by the following method: dissolving cobalt nitrate hexahydrate in water to obtain a precursor solution of cobalt nitrate; dissolving oxalic acid dihydrate in alcohol to obtain an alcoholic solution of oxalic acid; dropwise adding an alcoholic solution of oxalic acid into the precursor solution of cobalt nitrate, reacting to generate cobalt oxalate precipitate, and continuously stirring for a period of time; centrifuging, drying and crushing to obtain CoC2O4 powder; coC2O4 powder and sodium hypophosphite are mixed and put into a porcelain boat, the porcelain boat is put into a tubular furnace, N2 is introduced, and heating and heat preservation are conducted; and after the tubular furnace is cooled to room temperature, taking out solids in the porcelain boat, washing, centrifuging and drying to obtain the cobalt phosphide nano-catalyst. The catalyst has a high specific surface area, an ideal nano structure and abundant active sites, has excellent hydrogen evolution activity, and has good application prospects and large-scale popularization potential in the field of hydrogen production by electrolysis of water.

Description

TECHNICAL FIELD

[0001] The present application relates to phosphide catalyst technology, in particular to a cobalt phosphide nanocatalyst, a preparation method and application thereof. BACKGROUND

[0002] "Green hydrogen" produced by water electrolysis driven by renewable energy is considered as a core pillar of future energy systems due to its zero carbon emission and high energy density. However, water electrolysis technology for hydrogen production faces a key challenge in large-scale application, which is high energy consumption, mainly due to the kinetic slowness of cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), resulting in high overpotential. Therefore, developing efficient, stable and low-cost HER catalysts is crucial for significantly reducing energy consumption and promoting the development of green hydrogen economy.

[0003] Currently, noble metal catalysts such as platinum (Pt) based materials are recognized as the most efficient HER catalysts, but they are extremely scarce and costly, which seriously hinders the widespread commercial application of water electrolysis technology. From the perspective of resource cost and sustainability, some transition metal compounds, such as sulfides, nitrides and phosphides, have attracted widespread attention due to their unique electronic structure and potential excellent catalytic activity.

[0004] Cobalt phosphide (such as CoP, Co2P) has become one of the most promising candidates to replace Pt due to its unique metallic properties, adjustable electronic structure, good electrochemical stability, and excellent HER catalytic activity in a wide pH range. Its catalytic activity is derived from the moderate adsorption strength of phosphorus atoms to hydrogen and the optimization of water molecule dissociation and hydrogen desorption process by cobalt-phosphorus synergy. Although cobalt phosphide materials have great potential, the existing mainstream synthesis methods have significant challenges: high-temperature phosphating method is to heat treat cobalt source (oxide, hydroxide, etc.) and phosphorus source (such as sodium hypophosphite NaH2PO2) under inert atmosphere at high temperature (> 400℃). This method easily leads to severe particle agglomeration and sintering, and it is difficult to control the morphology; although the solvothermal / hydrothermal method can be carried out at a lower temperature, it often needs to use expensive and toxic organic phosphorus sources (such as trioctylphosphine TOP), not only the reaction time is long, but also the purity, crystallinity and potential for large-scale production of the product are limited; the electrodeposition / chemical plating method is usually limited to the preparation of thin films on specific substrates, which has limited specific surface area, complex composition and morphology control problems. SUMMARY

[0005] The present application aims at the above-mentioned problems, and provides a cobalt phosphide nanocatalyst, which has a high specific surface area, an ideal nanostructure, and abundant active sites, and has excellent hydrogen evolution activity.

[0006] It should be noted that, in the present application, unless otherwise specified, the specific meaning of "including" involved in the composition limitation and description includes both the open "including", "containing" and the like, and the closed "consisting of", "consisting" and the like.

[0007] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: S1, dissolving cobalt nitrate hexahydrate in water to obtain a precursor solution of cobalt nitrate; dissolving oxalic acid dihydrate in alcohol to obtain an alcohol solution of oxalic acid; S2, dropwise adding the alcohol solution of oxalic acid to the precursor solution of cobalt nitrate, stirring while dropping, and reacting to generate cobalt oxalate precipitate, and continuing to stir for a period of time; S3, centrifuging, drying and crushing the cobalt oxalate precipitate to obtain CoC2O4 powder; S4, mixing the CoC2O4 powder with sodium hypophosphite, and then placing the mixture in a porcelain boat, and placing the porcelain boat in a tube furnace and introducing N2, and heating and holding; S5, after the tube furnace is cooled to room temperature, the product is washed, centrifuged and dried to obtain a cobalt phosphide nanocatalyst.

[0008] Further, the alcohol in step S1 is one or more of anhydrous ethanol, ethylene glycol and isopropyl alcohol.

[0009] Further, the concentration of the precursor solution of cobalt nitrate in step S1 is 0.1-0.3 mol / L, for example, 0.1 mol / L, 0.2 mol / L or 0.3 mol / L; and the concentration of the alcohol solution of oxalic acid is 0.15-0.45 mol / L, for example, 0.15 mol / L, 0.3 mol / L or 0.45 mol / L.

[0010] Further, the use amount of the alcohol solution of oxalic acid and the precursor solution of cobalt nitrate in step S2 satisfies that the molar ratio of cobalt nitrate to oxalic acid is 1-3:1.5-4.5.

[0011] Further, the reaction temperature in step S2 is 20-25℃, and after the cobalt oxalate precipitate is generated, the stirring is continued for 10-12h.

[0012] Further, the centrifugal speed in step S3 is 8000-10000 r / min, and the centrifugal time is 8-10 min; the drying temperature is 50-60 ℃, and the drying time is 6-24 h. Further, the particle size of the CoC2O4 powder obtained by crushing in step S3 is 200-300 nm.

[0013] Further, the mass ratio of the CoC2O4 powder to sodium hypophosphite in step S4 is 1:1.5-3. By controlling the content of sodium hypophosphite, the phase (orthorhombic structure) of cobalt phosphide is controlled.

[0014] Further, the heating speed in step S4 is 3-5 ℃ / min, the heating temperature is 350-450 ℃, and the holding time is 2-4 h. The present application controls the apparent morphology and nanostructure of the catalyst by using a suitable heating rate and synthesis temperature.

[0015] Further, the washing in step S5 is alternating washing with ethanol and ultrapure water for 3-5 times, the drying temperature is 60-70 ℃, and the drying time is 6-24 h.

[0016] Another object of the present application also discloses a cobalt phosphide nano-catalyst prepared by the above method.

[0017] Further, the particle size of the cobalt phosphide nano-catalyst is 50-150 nm.

[0018] Further, the specific surface area of the cobalt phosphide nano-catalyst is 54-56 m 2 / g.

[0019] Another object of the present application also discloses the application of the cobalt phosphide nano-catalyst in the field of water electrolysis for hydrogen production.

[0020] Further, the cobalt phosphide nano-catalyst is particularly suitable for cathodic hydrogen evolution reaction.

[0021] Further, the cathodic hydrogen evolution reaction uses the cobalt phosphide nano-catalyst, and a mixed solution is prepared according to the ratio of ethylene glycol: deionized water: isopropyl alcohol: Nafion (5 wt.%) = 250:500:250:5, a dispersion liquid with a catalyst content of 2.3 mg / mL is prepared by using the above mixed solution, 25 uL of the dispersion liquid is dropped onto a carbon paper with a size of 1×1 cm, dried in a 60 ℃ drying oven, and tested for HER activity in a 1.0 M KOH solution, and the LSV curve scanning speed is 5 mV / s.

[0022] The cobalt phosphide nano-catalyst, the preparation method and the application thereof have the following advantages compared with the prior art: 1) The application discloses a method for preparing cobalt phosphide nanocatalyst by an oxalate phosphating method. Cobalt oxalate has the potential to be an ideal precursor. By a simple solution precipitation method, cobalt oxalate with high specific surface area and specific nanostructure can be obtained. When the cobalt oxalate is heated in an inert atmosphere, stepwise thermal decomposition occurs: first, the crystal water is lost, and then the pure cobalt metal particles are decomposed at a lower temperature (350-400 DEG C) and CO and CO2 gases are released. This process can generate a loose and porous elemental metal Co intermediate in situ. The structure of the elemental cobalt particle has a large specific surface area and rich diffusion channels, providing an ideal place for the subsequent phosphating reaction. When the cobalt oxalate is phosphated with NaH2PO2, the phosphine gas can more fully adsorb, penetrate and diffuse to the surface and interior of the cobalt particle structure. At the same time, the newly generated Co particles have high reactivity, and at a relatively low phosphating temperature, the cobalt phosphide catalyst with rich active sites and excellent mass transfer performance can be obtained.

[0023] The cobalt phosphide nanocatalyst prepared by the precursor phosphating method has the advantages of simple process, low cost, high efficiency, and small energy consumption. 2) The application realizes low-temperature and high-efficiency phosphating by synthesizing cobalt oxalate precursor with target morphology and generating a porous intermediate in situ. The prepared cobalt phosphide nanocatalyst has certain hydrogen evolution reaction activity. 3) The cobalt phosphide nanocatalyst prepared by the application is in the state of nanoparticles, with a particle size of 50-150 nm and a surface area of 54-56 m 2 / g, and has good stability.

[0024] The cobalt phosphide nanocatalyst has good application prospect and large-scale promotion potential in the field of water electrolysis hydrogen production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 X-ray diffraction pattern of the cobalt phosphide nanocatalyst of Example 3; Figure 2 Geometric area current activity graph (LSV curve of electrocatalytic HER) of the cobalt phosphide nanocatalyst of Example 3 and HER catalyst benchmark 60 wt.% Pt / C; Figure 3 Geometric area current activity graph (LSV curve of electrocatalytic OER) of the cobalt phosphide nanocatalyst of Example 3 and OER catalyst benchmark IrO2; Figure 4 Nitrogen isothermal adsorption-desorption curve graph of the cobalt phosphide nanocatalyst of Example 3; Figure 5 Transmission electron microscope (TEM) graph of the cobalt phosphide nanocatalyst of Example 3. DETAILED DESCRIPTION

[0026] Hereinafter, the present application will be further described with reference to examples. The description of technical features described below is based on representative embodiments, specific examples of the present application, but the present application is not limited to these embodiments, specific examples. Note that: Unless otherwise specified, the units used in the specification are international standard units, and the numerical values, numerical value ranges appearing in the present application should be understood to include systematic errors that are unavoidable in industrial production.

[0027] In the specification, the numerical value range indicated by "numerical value A ~ numerical value B" means a range including the end point numerical values A, B.

[0028] In the specification, the numerical value range indicated by "above" or "below" means a numerical value range including the number.

[0029] In the specification, the meaning indicated by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0030] In the specification, "optional" or "optionally" means that the use or non-use of certain substances, components, execution steps, applied conditions, etc.

[0031] In the specification, when "room temperature" or "room temperature" is used, the temperature can be 15-25 ℃.

[0032] In the specification, the reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained by purchase. Example 1

[0033] This example discloses a cobalt phosphide nanocatalyst prepared by oxalate phosphatization, and the specific preparation method is as follows: S1, dissolve cobalt nitrate hexahydrate in 100 ml water solution to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.1 mol / L; dissolve oxalic acid in 100 ml anhydrous ethanol solution to obtain an alcohol solution of oxalic acid, and the concentration of the alcohol solution of oxalic acid is 0.15 mol / L; S2, drop the alcohol solution of oxalic acid into the cobalt nitrate precursor solution, and stir at room temperature while dropping, and the reaction generates cobalt oxalate precipitate, and continue stirring for 10 h; S3, centrifuge the product obtained in step S2 at a centrifugal rate of 8000 r / min for 8 min; dry the obtained solid at 50 ℃ for 12 h to obtain CoC2O4 precipitate; S4, the CoC2O4 precipitate was manually ground in a agate mortar for 60 s to break the soft agglomeration and fully disperse the powder, and finally passed through a 300 mesh (about 48 pm) standard sieve to obtain a uniform loose powder. Transferred to a porcelain boat, 3 g of sodium hypophosphite was added and mixed, the porcelain boat was placed in a tube furnace, and nitrogen was introduced from the upstream at a flow rate of 50 mL / min, and the temperature was raised to 380 ℃ at a rate of 2 ℃ per minute, and kept for 2 h; S5, after the tube furnace cooled to room temperature, the mixture was taken out and washed by centrifugation, ultrapure water and ethanol alternately for 4 times, and then vacuum dried at 60 ℃ for 12 h, to prepare a cobalt phosphide nano-catalyst with a particle size of 50-150 nm. The oxalate precursor will form a porous cobalt elemental structure in situ under high-temperature inert gas environment, providing a high specific surface area substrate for cobalt phosphide, exposing more active sites, which is conducive to the adsorption and reaction of phosphine, thereby obtaining a cobalt phosphide nano-catalyst with hydrogen evolution activity. Example 2

[0034] This embodiment discloses a cobalt phosphide nano-catalyst prepared by oxalate phosphidation, and the specific preparation method is as follows: S1, dissolve cobalt nitrate hexahydrate in 100 ml of aqueous solution to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.1 mol / L; dissolve oxalic acid in 100 ml of ethylene glycol solution to obtain an oxalic acid alcohol solution, and the concentration of the oxalic acid alcohol solution is 0.15 mol / L; S2, drop the oxalic acid alcohol solution into the cobalt nitrate precursor solution, and stir while dropping at room temperature, to generate a cobalt oxalate precipitate, and continue stirring for 10 h; S3, centrifuge the product obtained in step S2 at a centrifugal rate of 8000 r / min for 8 min; and dry the obtained solid at 50 ℃ for 12 h to obtain a CoC2O4 precipitate; S4, the CoC2O4 precipitate was manually ground in a agate mortar for 60 s to break the soft agglomeration and fully disperse the powder, and finally passed through a 300 mesh (about 48 pm) standard sieve to obtain a uniform loose powder. Transferred to a porcelain boat, 3 g of sodium hypophosphite was added and mixed, the porcelain boat was placed in a tube furnace, and nitrogen was introduced from the upstream at a flow rate of 50 mL / min, and the temperature was raised to 380 ℃ at a rate of 2 ℃ per minute, and kept for 2 h; S5, after the tube furnace cooled to room temperature, the mixture was taken out and washed by centrifugation, ultrapure water and ethanol alternately for 4 times, and then vacuum dried at 60 ℃ for 12 h, to prepare a cobalt phosphide nano-catalyst with a particle size of 50-150 nm. The oxalate precursor will form a porous cobalt elemental structure in situ under high-temperature inert gas environment, providing a high specific surface area substrate for cobalt phosphide, exposing more active sites, which is conducive to the adsorption and reaction of phosphine, thereby obtaining a cobalt phosphide nano-catalyst with hydrogen evolution activity. Example 3

[0035] This embodiment discloses a cobalt phosphide nanocatalyst prepared by oxalate phosphatization, and the specific preparation method is as follows: S1, dissolve cobalt nitrate hexahydrate in 100 ml water solution to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.2 mol / L; dissolve oxalic acid in 100 ml anhydrous ethanol solution to obtain an oxalic acid alcohol solution, and the concentration of the oxalic acid alcohol solution is 0.3 mol / L; S2, drop the oxalic acid alcohol solution into the cobalt nitrate precursor solution, and stir at room temperature while dropping; the reaction generates cobalt oxalate precipitate, and continue to stir for 10 h; S3, centrifuge the product obtained in step S2 at a centrifugal rate of 9000 r / min for 9 min; dry the obtained solid at 50 ℃ for 12 h to obtain CoC2O4 precipitate; S4, manually grind the CoC2O4 precipitate in a marver for 60 s to break the soft agglomeration and fully disperse the powder, and finally pass through a 300 mesh (about 48 μm) standard sieve to obtain a uniform and loose powder. Transfer to a porcelain boat, add 4.5 g of sodium hypophosphite to mix, place the porcelain boat in a tube furnace, and pass nitrogen from the upstream at a flow rate of 50 mL / min, and heat to 400 ℃ at a rate of 3 ℃ per minute, and keep for 2 h; S5, after the tube furnace is cooled to room temperature, the mixture is taken out, washed by centrifugation, ultrapure water and ethanol alternately for 5 times, and then vacuum dried at 60 ℃ for 12 h to prepare a cobalt phosphide nanocatalyst, and the particle size is 50-150 nm. The oxalate precursor will form a porous cobalt elemental structure in situ under high temperature inert gas environment, providing a high specific surface area substrate for cobalt phosphide, exposing more active sites, which is beneficial to the adsorption and reaction of phosphine, so as to obtain a cobalt phosphide nanocatalyst with hydrogen evolution activity.

[0036] Figure 1 The X-ray diffraction (XRD) pattern of the cobalt phosphide catalyst of Example 3 confirms the successful conversion of the oxalate precursor to phosphide, and the three peaks are located at about 31.58, 40.72, and 48.11°, revealing that the cobalt phosphide nanocatalyst prepared by phosphatization of the oxalate precursor is an orthorhombic structure.

[0037] Figure 2Geometric area current activity plot (LSV curve of electrocatalysis HER) of cobalt phosphide nanocatalyst of Example 3 and HER catalyst benchmark 60 wt. % Pt / C. Test conditions: mixed solution was prepared according to the ratio of ethylene glycol: deionized water: isopropyl alcohol: Nafion (5 wt. %) = 250: 500: 250: 5, a dispersion liquid with a catalyst content of 2.3 mg / mL was prepared using the above mixed solution, 25 uL of the dispersion liquid was dropped onto carbon paper with a size of 1 x 1 cm, dried in a 60°C drying oven, and tested for HER activity in a 1.0 M KOH solution, and the LSV curve scan rate was 5 mV / s. By comparing the geometric area current density at the same potential, it can be seen that the geometric area current density value of the cobalt phosphide nanocatalyst prepared in this example is close to that of the HER benchmark 60 wt. % Pt / C catalyst, proving the superiority of the cobalt phosphide nanocatalyst of this example.

[0038] Figure 3 Geometric area current activity plot (LSV curve of electrocatalysis OER) of cobalt phosphide nanocatalyst of Example 3 and OER catalyst benchmark IrO2. Test conditions: mixed solution was prepared according to the ratio of ethylene glycol: deionized water: isopropyl alcohol: Nafion (5 wt. %) = 250: 500: 250: 5, a dispersion liquid with a catalyst content of 2.3 mg / mL was prepared using the above mixed solution, 1 mL of the dispersion liquid was dropped onto carbon paper with a size of 1 x 1 cm, dried in a 60°C drying oven, and tested for OER activity in a 1.0 M KOH solution, and the LSV curve scan rate was 5 mV / s. By comparing the geometric area current density at the same potential, it can be seen that the geometric area current density value of the cobalt phosphide nanocatalyst prepared by oxalate phosphating in this example exceeds that of the OER benchmark IrO2 catalyst, proving the superiority of the cobalt phosphide nanocatalyst of this example.

[0039] Figure 4 Nitrogen isothermal adsorption-desorption curve of cobalt phosphide nanocatalyst of Example 3. It can be seen that the curve presents the characteristics of type IV isotherm with a clear H3 type hysteresis loop, which indicates that the prepared catalyst has a typical mesoporous structure. The mesoporous structure is derived from the abundant pores created by gas release during the thermal decomposition process of the cobalt oxalate precursor. The BET specific surface area is between 54-56 m 2 / g.

[0040] Figure 5 Transmission electron microscopy (TEM) of cobalt phosphide nanocatalyst of Example 3. It can be seen that the synthesized cobalt phosphide presents a uniform distribution of nanoparticle morphology, the particle morphology tends to be approximately irregular polygon, and the particle size is concentrated between 50-150 nm. Example 4

[0041] The embodiment discloses a cobalt phosphide nanocatalyst prepared by oxalate phosphorization, and a specific preparation method is as follows: S1, dissolve cobalt nitrate hexahydrate in 100 ml of aqueous solution to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.2 mol / L; dissolve oxalic acid in 100 ml of isopropyl alcohol solution to obtain an oxalic acid alcohol solution, and the concentration of the oxalic acid alcohol solution is 0.3 mol / L; S2, drop the oxalic acid alcohol solution into the cobalt nitrate precursor solution, and stir at room temperature while dropping, so that cobalt oxalate precipitate is generated by reaction, and the stirring is continued for 12 hours; S3, centrifuge the product obtained in step S2 at a centrifugal rate of 9000 r / min for 9 minutes; and dry the obtained solid at 50 DEG C for 12 hours to obtain CoC2O4 precipitate; S4, manually grind the CoC2O4 precipitate in a marver for 60 seconds to break the soft agglomeration and fully disperse the powder, and finally pass the powder through a 300 mesh (about 48 μm) standard sieve to obtain a uniform and loose powder; transfer the powder into a porcelain boat, add 6 g of sodium hypophosphite into the porcelain boat, mix the powder and the sodium hypophosphite, place the porcelain boat in a tube furnace, pass nitrogen into the tube furnace from an upstream, the flow rate of the nitrogen is 50 mL / min, and the temperature is increased to 400 DEG C at a rate of 4 DEG C per minute, and keep the temperature for 3 hours; S5, after the tube furnace is cooled to room temperature, the mixture is taken out, washed by centrifugation, ultrapure water and ethanol alternately for 4 times, and dried at 60 DEG C under vacuum for 12 hours, so that a cobalt phosphide nanocatalyst is prepared, and the particle size of the cobalt phosphide nanocatalyst is 50-150 nm. The oxalate precursor can generate a porous cobalt elemental structure in situ under a high-temperature inert gas environment, so as to provide a high specific surface area substrate for the cobalt phosphide, expose more active sites, be beneficial to the adsorption and reaction of phosphine, and thus obtain the cobalt phosphide nanocatalyst with hydrogen evolution activity. Example 5

[0042] The embodiment discloses a cobalt phosphide nanocatalyst prepared by oxalate phosphorization, and a specific preparation method is as follows: S1, dissolve cobalt nitrate hexahydrate in 100 ml of aqueous solution to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.3 mol / L, dissolve oxalic acid in 100 ml of isopropyl alcohol solution to obtain an oxalic acid alcohol solution, and the concentration of the oxalic acid alcohol solution is 0.45 mol / L; S2, drop the oxalic acid alcohol solution into the cobalt nitrate precursor solution, and stir at room temperature while dropping, so that cobalt oxalate precipitate is generated by reaction, and the stirring is continued for 12 hours; S3, centrifuge the product obtained in step S2 at a centrifugal rate of 9000 r / min for 9 minutes; and dry the obtained solid at 50 DEG C for 12 hours to obtain CoC2O4 precipitate; S4, the CoC2O4 precipitate is manually ground in an agate mortar for 60 s to break up soft agglomeration and fully disperse the powder, and finally passed through a 300 mesh (about 48 pm) standard sieve to obtain a uniform loose powder. Transfer to a porcelain boat, while adding 6 g of sodium hypophosphite to mix, place the porcelain boat in a tube furnace, and pass nitrogen from upstream at a flow rate of 50 mL / min, heat at 4 ℃ per minute to 450 ℃, and hold for 4 h; S5, after the tube furnace is cooled to room temperature, the mixture is washed by centrifugation, ultrapure water and ethanol alternately 5 times, and then vacuum dried at 60 ℃ for 12 h to prepare a cobalt phosphide nano-catalyst with a particle size of 50-150 nm. The oxalate precursor will form a porous cobalt elemental structure in situ under high-temperature inert gas environment, providing a high specific surface area substrate for cobalt phosphide, exposing more active sites, which is conducive to the adsorption and reaction of phosphine, thereby obtaining a cobalt phosphide nano-catalyst with hydrogen evolution activity. Example 6

[0043] This embodiment discloses a cobalt phosphide nano-catalyst prepared by oxalate phosphidation, and the specific preparation method is as follows: S1, dissolve 100 ml of cobalt nitrate hexahydrate in water to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.3 mol / L; dissolve oxalic acid in 100 ml of isopropyl alcohol solution to obtain an oxalic acid alcohol solution, and the concentration of the oxalic acid alcohol solution is 0.45 mol / L; S2, add the oxalic acid alcohol solution dropwise to the cobalt nitrate precursor solution, and stir at room temperature while adding, and the reaction generates a cobalt oxalate precipitate, and continue stirring for 10 h; S3, centrifuge the product obtained in step S2 at a speed of 10000 r / min for 10 min; and dry the obtained solid at 60 ℃ for 12 h to obtain a CoC2O4 precipitate; S4, the CoC2O4 precipitate is manually ground in an agate mortar for 60 s to break up soft agglomeration and fully disperse the powder, and finally passed through a 300 mesh (about 48 pm) standard sieve to obtain a uniform loose powder. Transfer to a porcelain boat, while adding 6 g of sodium hypophosphite to mix, place the porcelain boat in a tube furnace, and pass nitrogen from upstream at a flow rate of 50 mL / min, heat at 4 ℃ per minute to 450 ℃, and hold for 4 h; S5, the mixture was taken out after the tube furnace was cooled to room temperature, washed by centrifugation, ultrapure water and ethanol alternately for 4 times, and then vacuum dried at 60℃ for 12 hours, to prepare cobalt phosphide nanocatalyst with a particle size of 50-150nm. The oxalate precursor can provide a high specific surface area substrate for cobalt phosphide under high-temperature inert gas environment, expose more active sites, be conducive to the adsorption and reaction of phosphine, and thus obtain cobalt phosphide nanocatalyst with hydrogen evolution activity. Example 7

[0044] The embodiment discloses a cobalt phosphide nanocatalyst prepared by oxalate phosphidization, and a specific preparation method is as follows: S1, dissolve 100 ml of cobalt nitrate hexahydrate in water to obtain a cobalt nitrate precursor solution, and the concentration of the cobalt nitrate precursor solution is 0.2 mol / L; dissolve oxalic acid in 100 ml of alcohol solution to obtain an alcohol solution of oxalic acid, and the concentration of the alcohol solution of oxalic acid is 0.3 mol / L; S2, drop the alcohol solution of oxalic acid into the cobalt nitrate precursor solution, and stir while dropping at room temperature; continue to stir for 10 hours to generate cobalt oxalate precipitate; S3, centrifuge the product obtained in step S2 at a centrifugal rate of 9000 r / min for 9 minutes; and dry the obtained solid at 50℃ for 12 hours to obtain CoC2O4 precipitate; S4, manually grind the CoC2O4 precipitate in a marver for 60 seconds to break the soft agglomeration and fully disperse the powder, and finally pass the powder through a 300 mesh (about 48 μm) standard sieve to obtain uniform and loose powder; transfer the powder to a porcelain boat, add 6 g of sodium hypophosphite to the porcelain boat, mix the two, place the porcelain boat in a tube furnace, pass nitrogen gas into the tube furnace from the upstream at a flow rate of 50 mL / min, and heat the tube furnace at a rate of 4℃ per minute to 450℃ and keep the temperature for 4 hours; S5, the mixture was taken out after the tube furnace was cooled to room temperature, washed by centrifugation, ultrapure water and ethanol alternately for 4 times, and then vacuum dried at 60℃ for 12 hours, to prepare cobalt phosphide nanocatalyst with a particle size of 50-150nm. The oxalate precursor can provide a high specific surface area substrate for cobalt phosphide under high-temperature inert gas environment, expose more active sites, be conducive to the adsorption and reaction of phosphine, and thus obtain cobalt phosphide nanocatalyst with hydrogen evolution activity. Example 8

[0045] The embodiment discloses a cobalt phosphide nanocatalyst prepared by oxalate phosphidization, and a specific preparation method is as follows: S1, dissolve cobalt nitrate hexahydrate in 100 ml of aqueous solution to obtain a cobalt nitrate precursor solution, the concentration of the cobalt nitrate precursor solution is 0.1 mol / L; dissolve oxalic acid in 100 ml of anhydrous ethanol solution to obtain an oxalic acid alcohol solution, the concentration of the oxalic acid alcohol solution is 0.15 mol / L; S2, drop the oxalic acid alcohol solution into the cobalt nitrate precursor solution, stir at room temperature while dropping, and the reaction generates cobalt oxalate precipitate, continue to stir for 10 h; S3, centrifuge the product obtained in step S2 at a speed of 8000 r / min for 8 min; dry the obtained solid at 50 ℃ for 12 h to obtain CoC2O4 precipitate; S4, manually grind the CoC2O4 precipitate in a marquis mortar for 60 s to break the soft agglomeration and fully disperse the powder, and finally pass through a 300 mesh (about 48 μm) standard sieve to obtain a uniform and loose powder. Transfer to a porcelain boat, add 4.5 g of sodium hypophosphite to it, and mix, place the porcelain boat in a tube furnace, and pass nitrogen gas from the upstream at a flow rate of 50 mL / min, and heat to 400 ℃ at a rate of 2 ℃ per minute, and keep the temperature for 2 h; S5, after the tube furnace cools to room temperature, remove the mixture, centrifuge, and wash with ultrapure water and ethanol alternately 4 times, and then vacuum dry at 60 ℃ for 12 h to prepare a cobalt phosphide nano-catalyst with a particle size of 50-150 nm. The oxalate precursor will form a porous cobalt elemental structure in situ under high-temperature inert gas environment, providing a high specific surface area substrate for cobalt phosphide, exposing more active sites, which is conducive to the adsorption and reaction of phosphine, thereby obtaining a cobalt phosphide nano-catalyst with hydrogen evolution activity.

[0046] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A cobalt phosphide nanocatalyst, characterized by, Prepared by the following method: S1, the cobalt nitrate hexahydrate is dissolved in water to obtain a precursor solution of cobalt nitrate; oxalic acid dihydrate is dissolved in alcohol to obtain an alcohol solution of oxalic acid; S2, the alcohol solution of oxalic acid is added dropwise to the precursor solution of cobalt nitrate, and stirred while adding, and the cobalt oxalate precipitate is generated by reaction, and the stirring is continued for a period of time; S3, the cobalt oxalate precipitate is centrifuged, dried and crushed to obtain CoC2O4 powder; S4, the CoC2O4 powder is mixed with sodium hypophosphite and then placed in a porcelain boat, the porcelain boat is placed in a tube furnace and N2 is introduced, heated and kept warm; S5, after the tube furnace is cooled to room temperature, the product is washed, centrifuged and dried to obtain a cobalt phosphide nanocatalyst.

2. The cobalt phosphide nanocatalyst according to claim 1, wherein, The alcohol solution of oxalic acid and the precursor solution of cobalt nitrate in step S2 meet the following requirements: the molar ratio of cobalt nitrate to oxalic acid is 1-3: 1.5-4.

5.

3. The cobalt phosphide nanocatalyst of claim 1, wherein the cobalt phosphide nanocatalyst has a size of about 1 nm to about 100 nm. The reaction temperature in step S2 is 20-25℃, and the stirring is continued for 10-12 h after the cobalt oxalate precipitate is generated.

4. The cobalt phosphide nanocatalyst of claim 1, wherein, The particle size of the CoC2O4 powder obtained by crushing in step S3 is 200-300 nm.

5. The cobalt phosphide nanocatalyst of claim 1, wherein the cobalt phosphide nanocatalyst has a particle size of about 1 nm to about 100 nm. The mass ratio of the CoC2O4 powder to sodium hypophosphite in step S4 is 1: 1.5-3.

6. The cobalt phosphide nanocatalyst of claim 1, wherein, The heating rate in step S4 is 3-5℃ / min, the heating temperature is 350-450℃, and the holding time is 2-4 h.

7. The cobalt phosphide nanocatalyst of claim 1, wherein the cobalt phosphide nanocatalyst has a particle size of about 1 nm to about 100 nm. The washing in step S5 is 3-5 times of alternating washing with ethanol and ultrapure water; And / or, the drying temperature is 60-70℃, and the drying time is 6-24 h.

8. A cobalt phosphide nanocatalyst, characterized in that, Prepared by the above method according to any one of claims 1-7.

9. The cobalt phosphide nanocatalyst of claim 8, wherein, The particle size of the cobalt phosphide nanocatalyst is 50-150 nm.

10. The cobalt phosphide nanocatalyst according to claim 8 or 9 is used in the field of hydrogen production by water electrolysis.

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