阅读说明：本技术 一种表面相工程改性的碳包裹氮化镍铁纳米球及其制备方法和应用 (Surface phase engineering modified carbon-coated nickel-iron nitride nanosphere and preparation method and application thereof ) 是由 范晓彬 陈启明 张凤宝 彭文朝 李阳 于 2021-09-13 设计创作，主要内容包括：本发明涉及一种表面相工程改性的碳包裹氮化镍铁纳米球及其制备方法和应用；将镍盐、铁盐、尿素、氟化铵和单宁酸加入去离子水中,超声分散至原料完全溶解,得到均一墨蓝色溶液；将步所得的均一溶液转移至高压反应釜于进行水热反应；将水热反应后产物进行离心处理,取沉淀物,置于真空烘箱干燥得粉末；将所得的粉末于氮气中700～900℃下高温退火,得到前驱体碳包裹镍铁合金纳米球；将得到的前驱体于氨气气氛中300～500℃下再次退火,最终得产物碳包裹氮化镍铁纳米球。本发明首次制备出过渡金属氮化物纳米球团簇,形貌均匀,孔洞丰富,极大提升了其高电流密度下析氧反应稳定性。(The invention relates to a carbon-coated nickel iron nitride nanosphere with surface phase engineering modification and a preparation method and application thereof; adding nickel salt, ferric salt, urea, ammonium fluoride and tannic acid into deionized water, and performing ultrasonic dispersion until the raw materials are completely dissolved to obtain a uniform dark blue solution; transferring the uniform solution obtained in the step (a) to a high-pressure reaction kettle for hydrothermal reaction; centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying in a vacuum oven to obtain powder; annealing the obtained powder at a high temperature of 700-900 ℃ in nitrogen to obtain precursor carbon-coated nickel-iron alloy nanospheres; and annealing the obtained precursor again at 300-500 ℃ in an ammonia atmosphere to finally obtain the carbon-coated nickel iron nitride nanosphere. The transition metal nitride nanosphere cluster prepared by the method for the first time is uniform in appearance and rich in holes, and the stability of the oxygen evolution reaction under high current density is greatly improved.)

1. A surface phase engineering modified carbon-coated nickel-iron nitride nanosphere is characterized in that a plurality of nickel-iron nitride nanospheres are coated by nitrogen-doped carbon to form a nanosphere cluster and have a porous structure; and nitrogen is doped into the carbon skeleton, the surface of the nickel-iron nitride nanosphere is nickel-iron nitride, the interior of the nickel-iron nitride nanosphere is a nickel-iron alloy phase, and the whole nitrogen content is 3-10%.

2. The carbon-coated nickel-iron nitride nanosphere of claim 1, wherein the surface nickel-iron ratio is 1.2: 1-2.0: 1, the bulk ferronickel ratio is 2.5: 1-3.0: 1; the diameter of a single nanosphere is 80-100 nanometers, the diameter of a cluster formed by a plurality of nanospheres is 600-900 nanometers, and the specific surface area and the pore volume are respectively 100-130 m²A sum of 0.15 to 0.25cm³/g。

3. The preparation method of the carbon-coated nickel-iron nitride nanosphere with the modified surface phase engineering is characterized by comprising the following steps of:

s1) adding nickel salt, ferric salt, urea, ammonium fluoride and tannic acid into deionized water, and performing ultrasonic dispersion for 20-60 minutes until the raw materials are completely dissolved to obtain a uniform dark blue solution;

s2) transferring the uniform solution obtained in the step S1) to a high-pressure reaction kettle for hydrothermal reaction at 100-130 ℃; centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying in a vacuum oven to obtain powder;

s3) annealing the powder obtained in the step S2) at high temperature of 700-900 ℃ in nitrogen to obtain precursor carbon-coated nickel-iron alloy nanospheres;

s4) annealing the precursor obtained in the step S3) again in an ammonia atmosphere at 300-500 ℃, and finally obtaining the carbon-coated nickel iron nitride nanosphere.

4. The method as set forth in claim 3, wherein the nickel salt of step S1) comprises one or more of nickel nitrate hexahydrate and nickel chloride hexahydrate.

5. The method as claimed in claim 3, wherein the iron salt of step S1) comprises one or more of ferric nitrate nonahydrate and ferric chloride hexahydrate.

6. The method as claimed in claim 3, wherein the concentration of the nickel salt solution in the step S1) is 0.03-0.15 mol/L, and the concentration ratio of the nickel salt solution to the iron salt solution is 3: 1; the concentration of urea and ammonium fluoride is 0.1-0.2 mol/L; the concentration of the tannic acid is 5-8 g/L.

7. The method as set forth in claim 3, wherein the hydrothermal reaction temperature in step S2) is 100-130 ℃, the heating rate is 3-10 ℃/min, and the time is 7-12 hours.

8. The method as claimed in claim 3, wherein the vacuum drying treatment time of the step S2) is 10 to 24 hours and the temperature is 60 to 80 ℃.

9. The method as claimed in claim 3, wherein the high temperature annealing temperature in step S3) is 700-900 ℃, the heating rate is 3-10 ℃/min, and the time is 2-3 hours.

10. The method according to claim 3, wherein the ammonia annealing temperature in step S4) is 300-500 ℃, the heating rate is 3-10 ℃/min, and the time is 6-10 hours.

Technical Field

The invention relates to a transition metal nitride nanosphere catalyst modified by surface phase engineering. In particular to a carbon-coated nickel iron nitride nanosphere with surface phase engineering modification and a preparation method and application thereof.

Background

The oxygen evolution reaction is an important half-reaction involved in various energy conversion and storage devices, especially electrocatalytic water electrolysis cells. However, oxygen evolution reactions involve slow kinetics of four electron transfer and often require high overpotentials to exhibit large current densities. Oxygen evolution reaction commercial electrocatalysts are typically noble metal materials such as ruthenium and iridium based electrocatalysts. The excessive cost of noble metals and their scarce reserves severely limit the use of noble metal-based materials in electrocatalytic oxygen evolution reactions. Transition metal nitride is theoretically an effective non-noble metal electrocatalyst for oxygen evolution reaction in electrocatalytic water decomposition, but due to limited electronic structure and active center, the transition metal nitride often has the disadvantages of activity attenuation under high current density, poor stability and the like, and the application of the transition metal nitride is greatly limited.

To solve the above problems, various morphologically and strategically modified transition metal nitride nanomaterials have been reported to be successfully prepared, wherein nickel iron nitride has been demonstrated to be a highly active oxygen evolution catalyst. Oxygen evolution reactions are considered to be catalyst surface related reactions and therefore strategies aimed at catalyst surface modification tend to have better results. However, the nickel-iron nitride nanospheres are easy to agglomerate in the nitriding process at a higher temperature, and the strategy of inducing surface phase transformation is very lacking, so that no literature report exists, and the surface phase engineering modification preparation of the nickel-iron nitride nanospheres is still challenging.

Therefore, the surface phase engineering modification of transition metal nitrides, especially nickel-iron nitrides, to improve the activity and stability of oxygen evolution reaction, especially the activity and stability under high current density, is a problem to be solved urgently.

Disclosure of Invention

The invention aims to solve the technical problem of providing a carbon-coated nickel iron nitride nanosphere catalyst which has a complete structure, a large specific surface area and surface phase engineering modification, a preparation method thereof and application thereof in electrocatalytic oxygen evolution reaction.

The technical scheme of the invention is as follows:

a surface phase engineering modified carbon-coated nickel-iron nitride nanosphere is characterized in that a plurality of nickel-iron nitride nanospheres are coated by nitrogen-doped carbon to form a nanosphere cluster and have a porous structure; and nitrogen is doped into the carbon skeleton, the surface of the nickel-iron nitride nanosphere is nickel-iron nitride, the interior of the nickel-iron nitride nanosphere is a nickel-iron alloy phase, and the whole nitrogen content is 3-10%.

The carbon-coated nickel-iron nitride nanospheres have a surface nickel-iron ratio of 1.2: 1-2.0: 1, the bulk ferronickel ratio is 2.5: 1-3.0: 1; the diameter of a single nanosphere is 80-100 nanometers, the diameter of a cluster formed by a plurality of nanospheres is 600-900 nanometers, and the specific surface area and the pore volume are respectively 100-130 m²A sum of 0.15 to 0.25cm³/g。

A preparation method of carbon-coated nickel iron nitride nanospheres with surface phase engineering modification comprises the following steps:

s1) adding nickel salt, ferric salt, urea, ammonium fluoride and tannic acid into deionized water, and performing ultrasonic dispersion for 20-60 minutes until the raw materials are completely dissolved to obtain a uniform dark blue solution;

s2) transferring the uniform solution obtained in the step S1) to a high-pressure reaction kettle for hydrothermal reaction at 100-130 ℃; centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying in a vacuum oven to obtain powder;

s3) annealing the powder obtained in the step S2) at high temperature of 700-900 ℃ in nitrogen to obtain precursor carbon-coated nickel-iron alloy nanospheres;

s4) annealing the precursor obtained in the step S3) again in an ammonia atmosphere at 300-500 ℃, and finally obtaining the carbon-coated nickel iron nitride nanosphere.

The nickel salt of the step S1) comprises one or more of nickel nitrate hexahydrate and nickel chloride hexahydrate.

The iron salt in the step S1) comprises one or more of ferric nitrate nonahydrate and ferric chloride hexahydrate.

The concentration of the nickel salt solution in the step S1) is 0.03-0.15 mol/L, and the concentration ratio of the nickel salt solution to the ferric salt solution is 3: 1; the concentration of urea and ammonium fluoride is 0.1-0.2 mol/L; the concentration of the tannic acid is 5-8 g/L.

The hydrothermal reaction temperature of the step S2) is 100-130 ℃, the heating rate is 3-10 ℃/min, and the time is 7-12 hours.

The vacuum drying treatment time of the step S2) is 10-24 hours, and the temperature is 60-80 ℃.

The high-temperature annealing temperature of the step S3) is 700-900 ℃, the heating rate is 3-10 ℃/min, and the time is 2-3 hours.

The annealing temperature of the ammonia gas in the step S4) is 300-500 ℃, the heating rate is 3-10 ℃/min, and the time is 6-10 hours.

The surface of the nickel-iron nitride nanosphere is biphase nickel-iron nitride (Fe)₂Ni₂N and FeNi₃N, the interior is ferronickel alloy namely FeNi₃。

Carrying out electrocatalysis oxygen evolution reaction by using the carbon-coated nickel iron nitride nanosphere modified by the surface phase engineering as a catalyst, and uniformly coating the carbon-coated nickel iron nitride nanosphere catalyst modified by the surface phase engineering on the substrate foamed nickel to be used as a working electrode; and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. The load density of the carbon-coated nickel-iron nitride nanosphere catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution; the test result shows that: the electrocatalyst has good catalytic performance of oxygen evolution reaction, and has a current density of 10mA/cm²Next, only about 220mV of overpotential is required; at a current density of 400mA/cm²Next, only about 340mV of overpotential is required (FIG. 8), and is superior to commercial ruthenium dioxide noble metal catalysts. The Faraday efficiency reaches more than 98 percent, which shows that the oxygen evolution reaction efficiency is very excellent (figure 9). In addition, at current densities approaching 800mA/cm²Next, with a stability of at least 36 hours, the current density remains at least 90% (fig. 10), fully demonstrating the significant increase in activity and stability of this strategy in oxygen evolution reactions, especially at high current densities.

The invention has the advantages that:

(1) the transition metal nitride nanosphere cluster prepared by the method for the first time is uniform in appearance and rich in holes, and the stability of the oxygen evolution reaction under high current density is greatly improved.

(2) The invention applies the phase transformation related to the surface phase engineering to the transition metal nitride for the first time, enhances the reaction activity of the active site and improves the efficiency of the electrocatalytic oxygen evolution reaction.

The design of the catalytic activity center, a two-phase nitride layer is designed on the surface of the nanosphere for the first time (fig. 1 and fig. 6), the electronic interaction between active sites is enhanced, and the catalytic activity of the two-phase nitride is improved, especially the catalytic activity under high current density (fig. 8 and fig. 9); secondly, the catalyst has a structure of carbon-coated nanosphere clusters, so that the surface area is increased, the collapse of the catalyst under the high current density is prevented (shown in figures 2-5), in an electro-catalytic oxygen evolution stability test (shown in figure 10), the current density is still kept above 90% after 36-hour test, and the extremely strong stability is shown.

Drawings

Fig. 1 is XRD charts of the carbon-coated nickel-iron nitride nanospheres and the precursor carbon-coated nickel-iron alloy nanospheres prepared in example 2.

Fig. 2 is an SEM image of the carbon-coated nickel-iron nitride nanospheres prepared in example 2.

Fig. 3 is a TEM image of carbon-coated nickel iron nitride nanospheres prepared in example 2.

Fig. 4 is an isothermal adsorption diagram of the carbon-coated nickel iron nitride nanospheres prepared in example 2.

Fig. 5 is a distribution diagram of the pore diameter of the carbon-coated nickel iron nitride nanosphere prepared in example 2.

Fig. 6 is the polarization curve of the electrocatalytic oxygen evolution reaction of the carbon-coated nickel iron nitride nanospheres prepared in example 2.

FIG. 7 is the XPS argon ion depth profile of carbon coated NiFeNi nanospheres prepared in example 2.

FIG. 8 is a graph showing the variation of the Ni/Fe ratio corresponding to FIG. 7 of the carbon-coated NiFeNi nanospheres prepared in example 2.

Figure 9 is the faradaic efficiency chart of the electrocatalytic oxygen evolution reaction of the carbon-coated nickel iron nitride nanospheres prepared in example 2.

Fig. 10 is a graph of the stability of the carbon-coated nickel iron nitride nanospheres prepared in example 2 at high current density.

Detailed Description

The carbon-coated nickel iron nitride nanosphere catalyst, and the preparation method and application thereof according to the present invention will be described in detail with reference to the following embodiments and accompanying drawings.

The invention discloses a preparation method of carbon-coated nickel iron nitride nanospheres, which comprises the following steps of:

s1) adding nickel salt, ferric salt, urea, ammonium fluoride and tannic acid into deionized water, and performing ultrasonic dispersion for 20-60 minutes until the raw materials are completely dissolved to obtain a uniform dark blue solution; wherein, the nickel salt and the ferric salt are more than one of nickel nitrate hexahydrate, nickel chloride hexahydrate, ferric nitrate nonahydrate and ferric chloride hexahydrate; the concentration of the nickel salt solution is 0.03-0.15 mol/L, and the concentration ratio of the nickel salt solution to the ferric salt solution is 3: 1. the concentration of urea and ammonium fluoride is 0.1-0.2 mol/L; the concentration of the tannic acid is 5-8 g/L.

S2) transferring the uniform solution obtained in the step S1) to a 25-100 ml high-pressure reaction kettle to perform hydrothermal reaction at 100-130 ℃; centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying in a vacuum oven to obtain powder; wherein the hydrothermal reaction temperature is 100-130 ℃, the heating rate is 3-10 ℃/min, and the time is 7-12 hours; the vacuum drying treatment time is 10-24 hours, and the temperature is 60-80 ℃.

S3) annealing the powder obtained in the step S2) at high temperature of 700-900 ℃ in nitrogen to obtain precursor carbon-coated nickel-iron alloy nanospheres; wherein the high-temperature annealing heating rate is 3-10 ℃/min, and the time is 2-3 hours.

S4) annealing the precursor obtained in the step S3) again in an ammonia atmosphere at 300-500 ℃, and finally obtaining the carbon-coated nickel iron nitride nanosphere; wherein the temperature rise rate in the annealing process is 3-10 ℃/min, and the time is 6-10 hours.

The carbon-coated nickel-iron nitride nanospheres prepared by the preparation method of the carbon-coated nickel-iron nitride nanospheres are ferronickel alloy with cubic crystal systemAnd nickel-iron nitride, wherein the surface nickel-iron ratio is 1.2-2.0, and the bulk nickel-iron ratio is 2.5-3.0. The diameter of a single nanosphere is 80-100 nanometers, the cluster diameter formed by a plurality of nanospheres is 600-900 nanometers, and the BET specific surface area and the pore volume are respectively 100-130 m²A sum of 0.15 to 0.25cm³/g。

Specific examples are given below:

example 1

(1) 0.9mmol of nickel nitrate hexahydrate, 0.3mmol of ferric nitrate nonahydrate, 3mmol of urea, 3mmol of ammonium fluoride and 0.15g of tannic acid are added into 30mL of deionized water, the concentration of nickel nitrate hexahydrate in the obtained solution is 0.03mol/L, the concentration of ferric nitrate nonahydrate is 0.01mol/L, the concentrations of urea and ammonium fluoride are 0.1mol/L, and the concentration of tannic acid is 5 g/L. And ultrasonically dispersing for 20 minutes to completely dissolve the raw materials in the deionized water until the solution becomes dark blue, thereby obtaining a uniform solution.

(2) Transferring the obtained uniform solution to a high-pressure reaction kettle, reacting for 7 hours at 100 ℃, and heating at a rate of 3 ℃/min; and centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying the precipitate in a vacuum oven at 60 ℃ for 10 hours to obtain powder.

(3) And (3) annealing the powder at the high temperature of 700 ℃ for 2 hours under the protection of nitrogen, heating at the rate of 3 ℃/min, and cooling to room temperature after the annealing is finished to obtain precursor carbon-coated ferronickel alloy nanospheres.

(4) And annealing the precursor carbon-coated nickel-iron alloy nanospheres for 6 hours again at 300 ℃ in an ammonia atmosphere, heating at the rate of 3 ℃/min, and finally cooling to room temperature to obtain the product carbon-coated nickel-iron nitride nanospheres.

(5) And uniformly coating the product catalyst on the substrate foamed nickel to be used as a working electrode, and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. Wherein the loading density of the catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution.

Example 2

(1) 1.8mmol of nickel nitrate hexahydrate, 0.6mmol of ferric nitrate nonahydrate, 4mmol of urea, 4mmol of ammonium fluoride and 0.2g of tannic acid are added into 30mL of deionized water, the concentration of nickel nitrate hexahydrate in the obtained solution is 0.06mol/L, the concentration of ferric nitrate nonahydrate is 0.03mol/L, the concentrations of urea and ammonium fluoride are 0.13mol/L, and the concentration of tannic acid is 6.67 g/L. And (4) carrying out ultrasonic dispersion for 40 minutes to completely dissolve the raw materials in the deionized water until the solution becomes dark blue, thus obtaining a uniform solution.

(2) Transferring the obtained uniform solution to a high-pressure reaction kettle, reacting for 10 hours at 120 ℃, and raising the temperature at a rate of 5 ℃/min; and centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying the precipitate in a vacuum oven at 70 ℃ for 20 hours to obtain powder.

(3) And (3) annealing the powder at the high temperature of 700 ℃ for 2 hours under the protection of nitrogen, heating at the rate of 5 ℃/min, and cooling to room temperature after the annealing is finished to obtain precursor carbon-coated ferronickel alloy nanospheres.

(4) And annealing the precursor carbon-coated nickel-iron alloy nanospheres for 8 hours again at 400 ℃ in an ammonia atmosphere, raising the temperature at the rate of 5 ℃/min, and finally cooling to room temperature to obtain the product carbon-coated nickel-iron nitride nanospheres. From the XRD pattern in FIG. 1, it can be seen that ferronickel and ferronickel nitride are present in the catalyst at the same time, and the ferronickel nitride corresponds to two phases, namely Fe₂Ni₂N and FeNi₃N, and no other impurity diffraction peak. As can be seen from the SEM picture in FIG. 2, the catalyst has a shape of a nanosphere cluster, the size of the nanosphere cluster is about 600-900 nm, and the nanosphere cluster is composed of a plurality of small nanospheres, and the size of the nanosphere cluster is about 80-100 nm. It can be seen from the TEM image in fig. 3 that the nanospheres in the catalyst are wrapped by the carbon to form nanosphere clusters rather than being clustered together. As can be seen from the nitrogen isothermal adsorption and desorption curve in FIG. 4 and the pore size distribution diagram in FIG. 5, the catalyst has a mesoporous structure with a pore size of about 4 nm and a large specific surface area.

From the XPS argon ion depth analysis result in FIG. 6 and the corresponding Ni/Fe ratio in FIG. 7, it can be seen that the Ni/Fe ratio on the surface of the catalyst is stabilized between 1.2-1.3, and from Table 1, it can be seen that the Ni/Fe ratios in the nickel-iron alloy precursor and the bulk phase of the product catalyst are both close to the theoretical value of 3, which indicates that the catalyst is a biphase nitride Fe on the surface₂Ni₂N and FeNi₃The coexistence of N provides excellent catalytically active sites. ByTable 2 can see that the Ni/Fe ratio in the precursor ferronickel alloy is also close to 3, indicating that the surface phase engineered biphasic nitride active site process of the product catalyst occurs during ammonia nitridation, consistent with the foregoing.

TABLE 1 precursor FeNi₃And the product catalyst FeNi₃Atomic percentages of the elements mapping in SEM and TEM of N.

TABLE 2 precursor FeNi₃The atomic percentage of each element was measured by XPS.

(5) And uniformly coating the product catalyst on the substrate foamed nickel to be used as a working electrode, and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. Wherein the loading density of the catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution. As can be seen from the polarization curve of the electrocatalytic oxygen evolution test in FIG. 8, the catalyst has excellent catalytic performance and reaches the current density of 100mA cm^–2Only about 300mV of over potential is needed, which is superior to that of the commercial ruthenium dioxide noble metal catalyst. From the catalyst of FIG. 9 at 50mA cm^–2The high selectivity of the faradaic efficiency to oxygen evolution reaction can be seen, and the faradaic efficiency reaches more than 98%. As can be seen from the long-term stability at high current density in FIG. 10, the catalyst has a high current density of about 770mA cm^–2The catalyst can maintain stability for at least 36 hours and has current attenuation less than 10 percent, which is superior to that of a commercial ruthenium dioxide noble metal catalyst.

Example 3

(1) 4.5mmol of nickel nitrate hexahydrate, 1.5mmol of ferric nitrate nonahydrate, 6mmol of urea, 6mmol of ammonium fluoride and 0.24g of tannic acid are added into 30mL of deionized water, the concentration of nickel nitrate hexahydrate in the obtained solution is 0.15mol/L, the concentration of ferric nitrate nonahydrate is 0.05mol/L, the concentrations of urea and ammonium fluoride are 0.2mol/L, and the concentration of tannic acid is 8 g/L. And (4) ultrasonically dispersing for 60 minutes to completely dissolve the raw materials in the deionized water until the solution becomes dark blue, so as to obtain a uniform solution.

(2) Transferring the obtained uniform solution to a high-pressure reaction kettle, reacting for 12 hours at 130 ℃, and heating at a speed of 10 ℃/min; and centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying the precipitate in a vacuum oven at 80 ℃ for 24 hours to obtain powder.

(3) Annealing the powder at the high temperature of 900 ℃ for 3 hours under the protection of nitrogen, heating at the rate of 10 ℃/min, and cooling to room temperature after the annealing is finished to obtain precursor carbon-coated ferronickel alloy nanospheres.

(4) And annealing the precursor carbon-coated nickel-iron alloy nanospheres for 10 hours again at 500 ℃ in an ammonia atmosphere, raising the temperature at a rate of 10 ℃/min, and finally cooling to room temperature to obtain the product carbon-coated nickel-iron nitride nanospheres.

(5) And uniformly coating the product catalyst on the substrate foamed nickel to be used as a working electrode, and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. Wherein the loading density of the catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution.

Example 4

(1) 1.8mmol of nickel chloride hexahydrate, 0.6mmol of ferric chloride hexahydrate, 4mmol of urea, 4mmol of ammonium fluoride and 0.2g of tannic acid are added into 30mL of deionized water, the concentration of nickel nitrate hexahydrate in the obtained solution is 0.06mol/L, the concentration of ferric nitrate nonahydrate is 0.03mol/L, the concentrations of urea and ammonium fluoride are 0.13mol/L, and the concentration of tannic acid is 6.67 g/L. And (4) ultrasonically dispersing for 20 minutes to completely dissolve the raw materials in the deionized water until the solution becomes dark blue, so as to obtain a uniform solution.

(2) Transferring the obtained uniform solution to a high-pressure reaction kettle, reacting for 7 hours at 100 ℃, and heating at a rate of 3 ℃/min; and centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying the precipitate in a vacuum oven at 60 ℃ for 10 hours to obtain powder.

(3) And (3) annealing the powder at the high temperature of 700 ℃ for 2 hours under the protection of nitrogen, heating at the rate of 3 ℃/min, and cooling to room temperature after the annealing is finished to obtain precursor carbon-coated ferronickel alloy nanospheres.

(4) And annealing the precursor carbon-coated nickel-iron alloy nanospheres for 6 hours again at 300 ℃ in an ammonia atmosphere, heating at the rate of 3 ℃/min, and finally cooling to room temperature to obtain the product carbon-coated nickel-iron nitride nanospheres.

(5) And uniformly coating the product catalyst on the substrate foamed nickel to be used as a working electrode, and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. Wherein the loading density of the catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution.

Example 5

(1) 1.8mmol of nickel chloride hexahydrate, 0.6mmol of ferric nitrate nonahydrate, 4mmol of urea, 4mmol of ammonium fluoride and 0.2g of tannic acid are added into 30mL of deionized water, the concentration of nickel nitrate hexahydrate in the obtained solution is 0.06mol/L, the concentration of ferric nitrate nonahydrate is 0.03mol/L, the concentrations of urea and ammonium fluoride are 0.13mol/L, and the concentration of tannic acid is 6.67 g/L. And (4) carrying out ultrasonic dispersion for 40 minutes to completely dissolve the raw materials in the deionized water until the solution becomes dark blue, thus obtaining a uniform solution.

(2) Transferring the obtained uniform solution to a high-pressure reaction kettle, reacting for 10 hours at 120 ℃, and raising the temperature at a rate of 5 ℃/min; and centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying the precipitate in a vacuum oven at 70 ℃ for 20 hours to obtain powder.

(3) And (3) annealing the powder at the high temperature of 700 ℃ for 2 hours under the protection of nitrogen, heating at the rate of 5 ℃/min, and cooling to room temperature after the annealing is finished to obtain precursor carbon-coated ferronickel alloy nanospheres.

(4) And annealing the precursor carbon-coated nickel-iron alloy nanospheres for 8 hours again at 400 ℃ in an ammonia atmosphere, raising the temperature at the rate of 5 ℃/min, and finally cooling to room temperature to obtain the product carbon-coated nickel-iron nitride nanospheres.

(5) The product catalyst is evenly coated on the substrate foamed nickel to be used as a working electrode,and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. Wherein the loading density of the catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution.

Example 6

(1) 1.8mmol of nickel nitrate hexahydrate, 0.6mmol of ferric chloride hexahydrate, 4mmol of urea, 4mmol of ammonium fluoride and 0.2g of tannic acid are added into 30mL of deionized water, the concentration of nickel nitrate hexahydrate in the obtained solution is 0.06mol/L, the concentration of ferric nitrate nonahydrate is 0.03mol/L, the concentrations of urea and ammonium fluoride are 0.13mol/L, and the concentration of tannic acid is 6.67 g/L. And (4) ultrasonically dispersing for 60 minutes to completely dissolve the raw materials in the deionized water until the solution becomes dark blue, so as to obtain a uniform solution.

(2) Transferring the obtained uniform solution to a high-pressure reaction kettle, reacting for 12 hours at 130 ℃, and heating at a speed of 10 ℃/min; and centrifuging the product after the hydrothermal reaction, taking the precipitate, and drying the precipitate in a vacuum oven at 80 ℃ for 24 hours to obtain powder.

(3) Annealing the powder at the high temperature of 900 ℃ for 3 hours under the protection of nitrogen, heating at the rate of 10 ℃/min, and cooling to room temperature after the annealing is finished to obtain precursor carbon-coated ferronickel alloy nanospheres.

(4) And annealing the precursor carbon-coated nickel-iron alloy nanospheres for 10 hours again at 500 ℃ in an ammonia atmosphere, raising the temperature at a rate of 10 ℃/min, and finally cooling to room temperature to obtain the product carbon-coated nickel-iron nitride nanospheres.

(5) And uniformly coating the product catalyst on the substrate foamed nickel to be used as a working electrode, and performing related tests of the electrocatalytic oxygen evolution reaction by adopting a standard three-electrode system and an electrochemical workstation. Wherein the loading density of the catalyst is 0.2-0.5 mg/cm²The electrolyte is potassium hydroxide solution.

The above description is only for the preferred embodiment of the present invention, but the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes and modifications without departing from the inventive concept of the present invention, which falls into the protection scope of the present invention.

While the methods and techniques of the present invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and/or modifications of the methods and techniques described herein may be made without departing from the spirit and scope of the invention. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and content of the invention. The invention belongs to the known technology.