阅读说明：本技术 一种多级孔道磷化钴/氮掺杂碳网络电催化剂的制备方法 (Preparation method of multistage pore cobalt phosphide/nitrogen-doped carbon network electrocatalyst ) 是由 陈道勇 李嫣然 杨瑞琪 于 2020-12-07 设计创作，主要内容包括：本发明属于电解水催化剂材料制备的技术领域,具体为一种多级孔道磷化钴/氮掺杂碳网络电催化剂的制备方法和应用。本发明首先在一维蠕虫状胶束上生长一层连续的Zn-Co-ZIFs纳米颗粒,该蠕虫状胶束/Zn-Co-ZIFs具有一定的刚性和随机曲率,从溶液中沉淀析出后可以堆积形成大孔网络。通过对干燥的堆积网络进行热分解、氧化、磷化处理并刻蚀掉氧化锌,得到具有多级孔道结构的磷化钴/氮掺杂碳网络电催化剂。基于包含介孔和大孔的多级孔道结构,该电催化剂在催化电解水制氢的过程中具有快速的物质传输能力；氮掺杂的碳网络具有良好的电子传输能力；同时一维次级结构使得大量的活性催化位点充分暴露,因此该电催化剂表现出优异的电催化析氢性能。(The invention belongs to the technical field of preparation of electrolytic water catalyst materials, and particularly relates to a preparation method and application of a multistage pore cobalt phosphide/nitrogen-doped carbon network electrocatalyst. The invention firstly grows a layer of continuous Zn-Co-ZIFs nano particles on a one-dimensional vermicular micelle, the vermicular micelle/Zn-Co-ZIFs has certain rigidity and random curvature, and can be deposited to form a macroporous network after being precipitated and separated from a solution. The cobalt phosphide/nitrogen-doped carbon network electrocatalyst with a hierarchical pore structure is obtained by carrying out thermal decomposition, oxidation and phosphorization treatment on the dried stacking network and etching away zinc oxide. Based on a multi-stage pore channel structure containing mesopores and macropores, the electrocatalyst has rapid material transmission capability in the process of catalyzing and electrolyzing water to prepare hydrogen; the nitrogen-doped carbon network has good electron transport capacity; meanwhile, a large number of active catalytic sites are fully exposed due to the one-dimensional secondary structure, so that the electrocatalyst has excellent electrocatalytic hydrogen evolution performance.)

1. A preparation method of a multistage pore cobalt phosphide/nitrogen-doped carbon network electrocatalyst is characterized by comprising the following specific steps:

(1) dissolving an amphiphilic block copolymer in methanol, dripping protonated deionized water by using an injection pump, then slowly dripping a DNA aqueous solution, mixing for more than 2 hours, continuously dripping sufficient protonated deionized water, and assembling the copolymer under the induction of DNA to form a core-shell polymer worm-like micelle; stabilizing for more than 12 hours, adding a cross-linking agent 1, 4-dibromobutane to cross-link the nuclear layer, finally collecting the wormlike micelles by high-speed centrifugation, and re-dispersing in methanol;

(2) mixing methanol dispersion liquid of the worm-like micelle, zinc nitrate hexahydrate and cobalt nitrate hexahydrate in methanol, adding methanol solution of 2-methylimidazole, shaking uniformly, standing at room temperature for 12-36 h, and growing a layer of uniform Zn-Co-ZIFs on the worm-like micelle; then precipitating from the solution to obtain a product worm-shaped micelle composite network, recording as a worm-shaped micelle/Zn-Co-ZIFs network, and drying in vacuum;

(3) heating the wormlike micelle/Zn-Co-ZIFs network obtained in the step (2) to 500-600 ℃ at a heating rate of 2-5 ℃/min in an argon environment, and calcining for 1-1.5 h; naturally cooling to below 100 ℃, introducing air, heating to 350-420 ℃ in the air at a heating rate of 3-5 ℃/min, calcining for 0.5-1 h, and converting metal ions into zinc oxide and cobaltosic oxide;

(4) placing sodium hypophosphite monohydrate and the intermediate product obtained in the step (3) into the same porcelain boat, placing the porcelain boat into a tube furnace, placing the sodium hypophosphite monohydrate into an upper air port, heating to 300-400 ℃ at a heating rate of 3-5 ℃/min in an argon environment, and calcining for 1-3 h; cooling to room temperature, taking out, etching zinc oxide with 2M hydrochloric acid, washing with deionized water and absolute ethyl alcohol, and vacuum drying to obtain a cobalt phosphide/nitrogen-doped carbon network with a hierarchical pore structure; the network is formed by stacking one-dimensional secondary structures and has a large number of mesoporous and macroporous structures.

2. The method according to claim 1, wherein in the step (1), the block copolymer is poly (ethylene glycol)-b-Poly (4-vinylpyridine) or poly (N, N-dimethylacrylamide)-b-The poly (4-vinylpyridine) has a degree of polymerization of the hydrophobic block poly (4-vinylpyridine) of 30 to 200 and a degree of polymerization of the hydrophilic block of 50 to 400.

3. The method according to claim 1, wherein in the step (1), the wormlike micelles have a diameter of 20 to 30 nm and a length of 500 nm to 3 μm.

4. The method according to claim 1, wherein in the step (1), the molar ratio of the 1, 4-dibromobutane to the 4-vinylpyridine repeating units is 0.05 to 0.5.

5. The method according to claim 1, wherein in the step (2), the molar ratio of the total amount of zinc nitrate hexahydrate plus cobalt nitrate hexahydrate to 2-methylimidazole is 1:3 to 1:5, and the molar ratio of zinc nitrate hexahydrate to cobalt nitrate hexahydrate is 1:1 to 1: 5.

6. The preparation method according to claim 1, wherein in the step (4), the mass ratio of the sodium hypophosphite monohydrate to the intermediate product obtained in the step (3) is 15: 1-20: 1.

7. A cobalt phosphide/nitrogen-doped carbon network electrocatalyst with a hierarchical pore channel structure, obtained by the preparation method as claimed in any one of claims 1 to 6.

8. The application of the cobalt phosphide/nitrogen-doped carbon network electrocatalyst with a hierarchical pore channel structure as claimed in claim 7 in catalysis of electrolysis of water-out hydrogen reaction.

Technical Field

The invention belongs to the technical field of preparation of electrocatalytic materials, and particularly relates to a preparation method of a multistage pore cobalt phosphide/nitrogen-doped carbon network.

Background

In recent years, based on the problems of over-development and use of fossil energy on a global scale and environmental climate change caused thereby, the search for clean and possibly renewable energy sources that can replace the conventional fossil energy sources is a hot spot of global attention. Hydrogen energy is an ideal substitute for traditional fossil energy as a clean energy source with high energy density. In all artificial hydrogen production ways, the hydrogen production by water electrolysis can effectively utilize unstable power such as wind power generation, photovoltaic power generation and the like and other surplus power, and is an environment-friendly hydrogen production mode. At present, the noble metal platinum is the most efficient catalyst for hydrogen evolution reaction in the water electrolysis process, and can realize large current density under a very low overpotential. However, due to their low reserves and high prices, large-scale use of platinum catalysts has been difficult to achieve, and in recent years much attention has been paid to non-noble metal based catalysts, mainly comprising transition metal sulfides, carbides, phosphides, nitrides and borides, etc. The theoretical catalytic activity of the transition metal phosphide (such as cobalt phosphide and nickel phosphide) is high, but the catalytic effect of the platinum catalyst is far from the catalytic effect when the transition metal phosphide is actually applied to the catalytic electrolysis of the water hydrogen evolution reaction. Therefore, how to optimize the structure of the transition metal phosphide to obtain excellent catalytic performance is one of the important problems to be solved urgently.

Many studies have shown that the complexation of transition metal phosphides with porous carbon networks is one of the most effective ways to carry out structural optimization. The novel porous material of covalent organic framework is an ideal precursor for preparing transition metal phosphide/carbon composite. Organic ligands uniformly distributed in a covalent organic framework can be calcined into a porous carbon network, and a large number of metal ions form phosphide nanoparticles dispersed in the carbon network. Nevertheless, most of the related works at present use bulk covalent organic framework crystals with the size of several hundred nanometers to several micrometers as precursors to prepare transition metal phosphide/carbon composites, and since the mesoporous size of such composites is usually less than 10 nm and the path of the mesopores is tortuous, phosphide nanoparticles inside the bulk composites are inevitably difficult to be effectively exposed, so that the catalytic performance of the catalyst is difficult to be further improved. Some improvements introduce one-dimensional organic materials such as carbon nanotubes and electrospun fibers, grow covalent organic frameworks on the surfaces of the carbon nanotubes and form networks, and the covalent organic frameworks are used as precursors to obtain the transition metal phosphide/carbon composite containing macropores and mesopores. However, these methods always have various problems such as great difficulty in the growth of the covalent organic framework, poor structure or few active sites due to large diameter of the one-dimensional structure, so that how to obtain a one-dimensional organic material which is beneficial to the growth of the covalent organic framework and has a very small diameter to construct a transition metal phosphide/carbon composite with an optimized structure is still a difficult problem.

Disclosure of Invention

The invention aims to provide a multi-stage pore cobalt phosphide/nitrogen-doped carbon network with excellent electrocatalytic hydrogen evolution performance, and a preparation method and application thereof.

The invention provides a cobalt phosphide/nitrogen-doped carbon network with a hierarchical pore structure, which is constructed by taking a worm-like micelle/Zn-Co-ZIFs (Zn-Co zeolitimidate frameworks) network as a precursor. Firstly, a layer of continuous Zn-Co-ZIFs nano-particles grows on a one-dimensional vermicular micelle, and the vermicular micelle/Zn-Co-ZIFs have certain rigidity and random curvature and can be deposited to form a macroporous network after being precipitated and separated from a solution. Carrying out thermal decomposition, oxidation and phosphorization treatment on the dried accumulation network, and etching away zinc oxide to obtain the cobalt phosphide/nitrogen-doped carbon network electrocatalyst with a hierarchical pore structure; it has excellent electrocatalytic hydrogen evolution performance. The preparation method comprises the following specific steps:

(1) dissolving a certain amount of amphiphilic block copolymer in methanol, dripping a certain amount of protonated deionized water by using an injection pump, then slowly dripping an aqueous solution of DNA, mixing for more than 2 hours, continuously dripping a sufficient amount of protonated deionized water, and assembling the copolymer under the induction of the DNA to form the core-shell structure polymer worm-like micelle; stabilizing for more than 12 hours, adding a cross-linking agent 1, 4-dibromobutane to cross-link the nuclear layer, finally collecting the wormlike micelles by high-speed centrifugation, and re-dispersing in methanol;

(2) mixing a methanol dispersion solution of the wormlike micelles, zinc nitrate hexahydrate and cobalt nitrate hexahydrate in methanol with a certain volume, adding a methanol solution of 2-methylimidazole, shaking uniformly, standing at room temperature for 12-36 hours, and growing a layer of uniform Zn-Co-ZIFs on the wormlike micelles; then precipitating from the solution to obtain a product worm-shaped micelle composite network, recording as a worm-shaped micelle/Zn-Co-ZIFs network, and drying in vacuum;

(3) heating the wormlike micelle/Zn-Co-ZIFs network obtained in the step (2) to 500-600 ℃ at a heating rate of 2-5 ℃/min in an argon environment, and calcining for 1-1.5 h; naturally cooling to below 100 ℃, introducing air, heating to 350-420 ℃ in the air at a heating rate of 3-5 ℃/min, calcining for 0.5-1 h, and converting metal ions into zinc oxide and cobaltosic oxide;

(4) placing sodium hypophosphite monohydrate and the intermediate product obtained in the step (3) into the same porcelain boat, placing the porcelain boat into a tube furnace, placing the sodium hypophosphite monohydrate into an upper air port, heating to 300-400 ℃ at a heating rate of 3-5 ℃/min in an argon environment, and calcining for 1-3 h; and cooling to room temperature, taking out, etching the zinc oxide by using 2M hydrochloric acid, washing by using deionized water and absolute ethyl alcohol, and drying in vacuum to obtain the cobalt phosphide/nitrogen-doped carbon network with the hierarchical pore structure.

In step (1) of the present invention, the block copolymer is poly (ethylene glycol)-b-Poly (4-vinylpyridine) or poly (N, N-dimethylacrylamide)-b-The poly (4-vinylpyridine) has a degree of polymerization of the hydrophobic block poly (4-vinylpyridine) of 30 to 200 and a degree of polymerization of the hydrophilic block of 50 to 400.

In the step (1), the wormlike micelle has a diameter of 20-30 nm and a length of 500 nm-3 μm.

In the step (1), the molar ratio of the 1, 4-dibromobutane to the 4-vinylpyridine repeating unit is 0.05-0.5, so that the crosslinking degree of the poly (4-vinylpyridine) is controlled to be 10-100%.

In the step (2), the molar ratio of the total amount of zinc nitrate hexahydrate and cobalt nitrate hexahydrate to 2-methylimidazole is 1: 3-1: 5, and the molar ratio of zinc nitrate hexahydrate to cobalt nitrate hexahydrate is 1: 1-1: 5. The mol ratio of zinc nitrate hexahydrate and cobalt nitrate hexahydrate is changed, so that the contents of zinc ions and cobalt ions in Zn-Co-ZIFs are controlled, and the porous structure and the cobalt phosphide content of a final product are directly influenced.

In step (3) of the present invention, the calcination procedure converts the metal ions into zinc oxide and cobaltosic oxide.

In the step (4), the mass ratio of the sodium hypophosphite monohydrate to the intermediate product obtained in the step (3) is 15: 1-20: 1. The aim is to convert cobaltosic oxide into cobalt phosphide without the zinc oxide reacting.

The method comprises the steps of growing a layer of uniform Zn-Co-ZIFs on a worm-shaped micelle with the diameter of 20-30 nm, taking the worm-shaped micelle/Zn-Co-ZIFs network as a precursor, and obtaining a cobalt phosphide/nitrogen-doped carbon network with a large number of mesoporous and macroporous structures after thermal decomposition-oxidation-phosphorization treatment and dilute hydrochloric acid etching of zinc oxide, wherein the network is formed by stacking one-dimensional secondary structures.

The preparation method is simple, the calcination temperature is low, and the requirements on experimental conditions are not high. The prepared product contains a multi-level pore channel structure with mesopores and macropores, and has quick material transmission capability when being used as an electrocatalyst in the process of catalyzing and electrolyzing water to prepare hydrogen; the nitrogen-doped carbon network has good electron transport capacity; while the one-dimensional secondary structure leaves a large number of active catalytic sites fully exposed. The network can be used for catalyzing electrolytic water hydrogen evolution reaction, achieves specific current density under a very small overpotential and shows very high catalytic activity.

Drawings

FIG. 1 is a schematic scanning electron microscope of the worm-like micelle/Zn-Co-ZIFs network in example 1.

FIG. 2 is a schematic transmission electron micrograph showing a partial detail of a cobalt phosphide/nitrogen-doped carbon network in example 2.

FIG. 3 is a scanning electron micrograph of the cobalt phosphide/nitrogen-doped carbon network of example 3.

FIG. 4 shows the cobalt phosphide/nitrogen-doped carbon network of 0.5M H in examples 1, 2 and 3₂SO₄The electrocatalytic hydrogen production performance diagram in (1).

FIG. 5 is a graph of the electrocatalytic hydrogen production performance of the cobalt phosphide/nitrogen-doped carbon network in 1M KOH in examples 1, 2 and 3.

Detailed Description

The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.

Example 1, zinc nitrate hexahydrate and cobalt nitrate hexahydrate at a 1:2 molar ratio a cobalt phosphide/nitrogen doped carbon network was prepared.

The first step is as follows: a wormlike micelle methanol solution with a concentration of 1 mg/mL was prepared, and 16 mL of this solution was added to 164 mL of anhydrous methanol.

The second step is that: 0.2 g of zinc nitrate hexahydrate and 0.388 g of cobalt nitrate hexahydrate were weighed out and dissolved in the methanol solution of the first step.

The third step: and (2) weighing 0.656 g of 2-methylimidazole, dissolving in 20 mL of anhydrous methanol, pouring the solution into the mixed solution obtained in the second step, uniformly shaking, standing at room temperature for 24 h, pouring out supernatant, collecting precipitate, washing the precipitate with methanol for three times, dispersing in water, and carrying out freeze vacuum drying for 24 h to obtain the worm-like micelle/Zn-Co-ZIFs network.

The fourth step: weighing 100 mg of the wormlike micelle/Zn-Co-ZIFs network prepared in the third step, placing the wormlike micelle/Zn-Co-ZIFs network in a porcelain boat, placing the porcelain boat in a tube furnace, heating to 500 ℃ at the heating rate of 2 ℃/min under the argon environment, calcining for 1 h, naturally cooling to below 100 ℃, introducing air, heating to 350 ℃ at the heating rate of 3 ℃/min in the air, and calcining for 1 h.

The fifth step: weighing 40 mg of the product obtained in the fourth step, placing the product in a porcelain boat, placing 80 mg of sodium hypophosphite monohydrate in the same porcelain boat at a distance of 3 cm, placing the porcelain boat in a tube furnace, placing the sodium hypophosphite monohydrate in an air inlet, heating to 350 ℃ at a heating rate of 3 ℃/min in an argon environment, calcining for 2 hours, cooling to room temperature, taking out, etching zinc oxide with 2M hydrochloric acid, washing with deionized water and absolute ethyl alcohol, and drying in vacuum to obtain the cobalt phosphide/nitrogen doped carbon network with the hierarchical pore structure.

And a sixth step: weighing 10 mg of sample, dispersing in 1mL of mixed solution of absolute ethyl alcohol and deionized water (the volume ratio of the absolute ethyl alcohol to the deionized water is 17: 3), adding 10 muL of Nafion solution with the mass fraction of 5%, ultrasonically dispersing for 10min,dripping 4 μ L of the above dispersion solution on glassy carbon electrode, naturally drying, and respectively using the glassy carbon electrode as working electrode in three-electrode system at 0.5M H₂SO₄And the hydrogen production performance of the electrolyzed water is tested in a 1M KOH electrolyte solution, and the result shows that the sample is 0.5M H₂SO₄To reach a current density of 10 mA cm^-2The desired overpotential was 127mV, and a current density of 10 mA cm in 1M KOH was achieved^-2The desired overpotential was 125 mV.

Example 2 a cobalt phosphide/nitrogen-doped carbon network was prepared with a molar ratio of zinc nitrate hexahydrate to cobalt nitrate hexahydrate of 1: 3.

The first step is as follows: a wormlike micelle methanol solution with a concentration of 1 mg/mL was prepared, and 16 mL of this solution was added to 164 mL of anhydrous methanol.

The second step is that: 0.15g of zinc nitrate hexahydrate and 0.436 g of cobalt nitrate hexahydrate were weighed out and dissolved in the methanol solution of the first step.

The third step: and (2) weighing 0.656 g of 2-methylimidazole, dissolving in 20 mL of anhydrous methanol, pouring the solution into the mixed solution obtained in the second step, uniformly shaking, standing at room temperature for 24 h, pouring out supernatant, collecting precipitate, washing the precipitate with methanol for three times, dispersing in water, and carrying out freeze vacuum drying for 24 h to obtain the worm-like micelle/Zn-Co-ZIFs network.

The fourth step: weighing 100 mg of the wormlike micelle/Zn-Co-ZIFs network prepared in the third step, placing the wormlike micelle/Zn-Co-ZIFs network in a porcelain boat, placing the porcelain boat in a tube furnace, heating to 500 ℃ at the heating rate of 2 ℃/min under the argon environment, calcining for 1 h, naturally cooling to below 100 ℃, introducing air, heating to 350 ℃ at the heating rate of 3 ℃/min, and calcining for 1 h.

The fifth step: weighing 40 mg of the product obtained in the fourth step, placing the product in a porcelain boat, placing 80 mg of sodium hypophosphite monohydrate in the same porcelain boat at a distance of 3 cm, placing the porcelain boat in a tube furnace, placing the sodium hypophosphite monohydrate in an air inlet, heating to 350 ℃ at a heating rate of 3 ℃/min in an argon environment, calcining for 2 hours, cooling to room temperature, taking out, etching zinc oxide with 2M hydrochloric acid, washing with deionized water and absolute ethyl alcohol, and drying in vacuum to obtain the cobalt phosphide/nitrogen doped carbon network with the hierarchical pore structure.

And a sixth step: weighing 10 mg of sample, dispersing in 1mL of mixed solution of absolute ethyl alcohol and deionized water (the volume ratio of the absolute ethyl alcohol to the deionized water is 17: 3), adding 10 muL of Nafion solution with the mass fraction of 5%, ultrasonically dispersing for 10min, dripping 4 muL of the dispersion on a glassy carbon electrode, naturally drying, and respectively placing the glassy carbon electrode as a working electrode in a three-electrode system at 0.5M H₂SO₄And the hydrogen production performance of the electrolyzed water is tested in a 1M KOH electrolyte solution, and the result shows that the sample is 0.5M H₂SO₄To reach a current density of 10 mA cm^-2The desired overpotential was 98mV, and a current density of 10 mA cm in 1M KOH was achieved^-2The desired overpotential was 118 mV.

Example 3 a cobalt phosphide/nitrogen-doped carbon network was prepared with a molar ratio of zinc nitrate hexahydrate to cobalt nitrate hexahydrate of 1: 5.

The first step is as follows: a wormlike micelle methanol solution with a concentration of 1 mg/mL was prepared, and 16 mL of this solution was added to 164 mL of anhydrous methanol.

The second step is that: 0.1g of zinc nitrate hexahydrate and 0.485 g of cobalt nitrate hexahydrate were weighed and dissolved in the methanol solution of the first step.

The third step: and (2) weighing 0.656 g of 2-methylimidazole, dissolving in 20 mL of anhydrous methanol, pouring the solution into the mixed solution obtained in the second step, uniformly shaking, standing at room temperature for 24 h, pouring out supernatant, collecting precipitate, washing the precipitate with methanol for three times, dispersing in water, and carrying out freeze vacuum drying for 24 h to obtain the worm-like micelle/Zn-Co-ZIFs network.

The fourth step: weighing 100 mg of the wormlike micelle/Zn-Co-ZIFs network prepared in the third step, placing the wormlike micelle/Zn-Co-ZIFs network in a porcelain boat, placing the porcelain boat in a tube furnace, heating to 500 ℃ at the heating rate of 2 ℃/min under the argon environment, calcining for 1 h, naturally cooling to below 100 ℃, introducing air, heating to 350 ℃ at the heating rate of 3 ℃/min, and calcining for 1 h.

The fifth step: weighing 40 mg of the product obtained in the fourth step, placing the product in a porcelain boat, placing 80 mg of sodium hypophosphite monohydrate in the same porcelain boat at a distance of 3 cm, placing the porcelain boat in a tube furnace, placing the sodium hypophosphite monohydrate in an air inlet, heating to 350 ℃ at a heating rate of 3 ℃/min in an argon environment, calcining for 2 hours, cooling to room temperature, taking out, etching zinc oxide with 2M hydrochloric acid, washing with deionized water and absolute ethyl alcohol, and drying in vacuum to obtain the cobalt phosphide/nitrogen doped carbon network with the hierarchical pore structure.

And a sixth step: weighing 10 mg of sample, dispersing in 1mL of mixed solution of absolute ethyl alcohol and deionized water (the volume ratio of the absolute ethyl alcohol to the deionized water is 17: 3), adding 10 muL of Nafion solution with the mass fraction of 5%, ultrasonically dispersing for 10min, dripping 4 muL of the dispersion on a glassy carbon electrode, naturally drying, and respectively placing the glassy carbon electrode as a working electrode in a three-electrode system at 0.5M H₂SO₄And the hydrogen production performance of the electrolyzed water is tested in a 1M KOH electrolyte solution, and the result shows that the sample is 0.5M H₂SO₄To reach a current density of 10 mA cm^-2The desired overpotential was 145mV, reaching a current density of 10 mA cm in 1M KOH^-2The desired overpotential is 131 mV.

The above description is a typical embodiment of the present invention, but the present invention should not be limited to the disclosure of the embodiment. Therefore, equivalents and modifications may be made without departing from the spirit of the disclosure to fall within the scope of the invention.