CN111437864B - High-dispersion Cu/NC nano-cluster catalyst and preparation method thereof - Google Patents

High-dispersion Cu/NC nano-cluster catalyst and preparation method thereof Download PDF

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CN111437864B
CN111437864B CN202010303795.9A CN202010303795A CN111437864B CN 111437864 B CN111437864 B CN 111437864B CN 202010303795 A CN202010303795 A CN 202010303795A CN 111437864 B CN111437864 B CN 111437864B
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CN111437864A (en
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李光兰
徐晓存
曹硕
路中发
王新
田伟东
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Dalian University of Technology
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    • Y02E60/50—Fuel cells

Abstract

High-dispersion Cu/NC nano-cluster catalystA chemical agent and a preparation method thereof belong to the technical field of energy materials and electrochemistry. The nano cluster catalyst is g-C which is cheap and easy to obtain 3 N 4 And as a carrier, mixing an organic ligand serving as a metal complex and a metal copper salt serving as a Cu precursor, performing high-temperature calcination treatment at the temperature of 500-1100 ℃ for 0.2-48 h, etching the calcined material in an acid solution, washing and drying to obtain the Cu/NC electrocatalyst containing the highly dispersed Cu nanoclusters. By regulating Cu precursor, g-C 3 N 4 The proportion of the organic ligand and the calcination temperature and time can control the morphology and the pore structure of the catalyst, and the catalyst with excellent ORR performance is obtained through optimization. The preparation method is simple, the raw materials are low in price, and the prepared catalyst is good in stability and high in activity and can realize large-scale production.

Description

High-dispersion Cu/NC nano-cluster catalyst and preparation method thereof
Technical Field
The invention belongs to the technical field of energy materials and electrochemistry, relates to a cathode oxygen reduction reaction electrocatalyst, and particularly relates to a high-dispersion Cu/NC nano-cluster structure catalyst and a preparation method thereof.
Background
Fuel cells are the hot spot of research by researchers at home and abroad in recent years. However, the cathode Oxygen Reduction Reaction (ORR) of fuel cells presents a core challenge of slow kinetics. At present, the ORR catalyst with the best performance and the most widely used fuel cell is a Pt-based catalyst, but the Pt-based catalyst has poor stability, high price and limited Pt reserves, and the large-scale commercial use of the fuel cell is limited, so that the development of the catalyst with higher catalytic activity and stability, corrosion resistance and low cost has important practical significance and application value.
Of the several earth-abundant transition metals, copper-based materials are of great interest because of their tunable properties and low cost. The electronic structure of copper can be tuned by the size, oxidation state, and interaction with other doping elements of the copper nanoparticles. For example, kang et al [ Journal of Alloys and Compounds, 2019,795,462-470] reported that nitrogen-doped carbon with bimetallic intercalation of Cu and Co can be an effective ORR electrocatalyst, wherein the incorporation of a Cu precursor into a Co-based zeolite imidazolate framework precursor can not only synergistically enhance the activity of Co, but also increase the nitrogen content in the catalyst, which can create more active sites, thereby increasing ORR activity. However, the stability and activity of the compound are still required to be improved greatly to meet the practical application.
In order to achieve high efficiency catalysis, the preparation of materials into ultra-high dispersion nanocluster catalysts is one of the most direct and effective strategies. The nano-cluster is an ultra-small metal nano-particle formed by gathering several to hundreds of metal atoms, the particle diameter of the nano-cluster is about 2nm, and the size effect ensures that the material has special molecular-like property. For example, zuo et al adv. Mater.2017,29,1606200 report an electrode material which uses copper foam as a carrier and is compounded by sub-nano copper clusters and a quasi-amorphous metal sulfide, and the electrode material is found to have high-efficiency hydrogen evolution and oxygen evolution catalytic activities. The sub-nanometer copper clusters are thought to be capable of effectively inducing redistribution of charges on the surface of the material and promoting dissociation and adsorption of water molecules on the surface of the material in the catalysis process besides the catalytic activity of the quasi-amorphous metal sulfide. This is the first report on the promotion of sub-nano copper clusters on water splitting reactions. To our knowledge, however, studies of copper nanoclusters on catalytic ORR have not been reported.
Disclosure of Invention
Aiming at the defects of the prior art, the invention designs and prepares a Cu/NC electrocatalyst with a high-dispersion nanocluster structure and a preparation method thereof. In the invention, the organic ligand is used for complexing with the metallic copper, which is beneficial to preventing the metallic copper from agglomerating, so that a Cu nano-cluster structure is formed on the surface of the catalyst. Using porous g-C 3 N 4 As carriers, facilitating the addition of catalystSpecific surface area, richness of the pore structure of the catalyst, and exposure of more active sites, in addition g-C 3 N 4 The higher the N content, this leads to more defect active sites in the catalyst. Therefore, the catalyst prepared by the invention is a Cu/NC nanocluster catalyst which is porous and has high active site density. The catalyst has simple preparation method and low cost, and can be used as an excellent substitute of a noble metal Pt-based catalyst to be put into industrial production.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
a high-dispersion Cu/NC nano-cluster catalyst is prepared from cheap and easily available g-C 3 N 4 The support is a Cu/NC electrocatalyst containing highly dispersed Cu nanoclusters, which is obtained by mixing an organic ligand as a metal complex and a copper metal salt as a Cu precursor, followed by high temperature calcination and appropriate post-treatment. By regulating the Cu precursor, g-C 3 N 4 The proportion of the organic ligand to the organic ligand, the calcination temperature and time can control the morphology and the pore structure of the catalyst, and the catalyst with excellent ORR performance can be obtained through optimization.
A preparation method of a high-dispersion Cu/NC nano-cluster catalyst comprises the following steps:
in the first step, the g-C is treated by a microwave method and a heat treatment method 3 N 4 Precursor, preparation of g-C 3 N 4 (ii) a G to C 3 N 4 Adding into solvent for dispersion to obtain g-C 3 N 4 And (3) dispersing the mixture.
Secondly, adding copper salt and organic ligand into a solvent to obtain a mixed solution, and adding the mixed solution into the g-C 3 N 4 And drying the dispersion liquid to obtain a precursor solid material. The molar ratio of the copper salt to the organic ligand is 1.
And thirdly, calcining the precursor solid material in an inert atmosphere, raising the temperature to 500-1100 ℃ according to a room temperature program, carrying out constant temperature treatment for 0.2-48 h, carrying out etching treatment on the calcined material in an acid solution, washing and drying to obtain the target catalyst.
In the first stepg-C 3 N 4 The precursor is one or more of melamine, urea and dicyanodiamine.
In the second step, the organic ligand is one or more of Cu ligands such as phenanthroline, 2' -bipyridine, ethylene diamine tetraacetic acid, ethylenediamine, glycine and the like. The copper salt is one or more of copper nitrate, copper sulfate and copper chloride.
The first step solvent is one or more of water, ethanol, glycol and the like; the solvent in the second step is one or more of water, ethanol, glycol, etc.
The drying method in the second step comprises vacuum drying, air atmosphere drying and inert atmosphere drying, wherein the drying temperature is 50-150 ℃, and the drying time is 5-48 h.
The temperature programming rate of the calcination in the third step is 2-30 ℃ min -1 。
And the acid solution used in the etching in the third step is one or more of sulfuric acid, hydrochloric acid, nitric acid and other acids. The concentration of the acid solution is 0.1-10 mol L -1 The etching time is 1-48 h, and the etching temperature is 50-120 ℃.
The drying method in the third step comprises vacuum drying, air atmosphere drying, inert atmosphere drying and freeze drying, wherein the drying temperature is-20-300 ℃, and the drying time is 5-60 hours.
Compared with the prior art, the ultra-high dispersion nanocluster structure Cu/NC catalyst and the preparation method have the following advantages:
(1) The g-C catalyst with the ultra-high dispersion nanocluster structure prepared by the method is used 3 N 4 The nitrogen source can be used as both carbon source and nitrogen source, which is beneficial to improving the nitrogen content in the catalyst and improving the ORR reaction activity. Two-dimensional plane g-C 3 N 4 The graphene-like lamellar layer can be generated by aggregation in the calcining process, the specific surface area is large, the conductivity is high, the mass transfer and conductivity requirements of the material can be met, and the catalytic performance of the material is ensured.
(2) The ultra-high dispersion nanocluster structure Cu/NC catalyst prepared by the method is added with an organic ligand as metallic copperIonic complexes which promote the complexation and uniform anchoring of copper ions to g-C 3 N 4 In the layer, the aggregation and agglomeration of metal particles in the calcining process are effectively prevented, so that the active site metal nanoparticles in the catalyst are distributed more uniformly and are smaller, and the activity and the stability of the catalyst are improved.
(3) The ultra-high dispersion nanocluster structure Cu/NC catalyst g-C prepared by the method of the invention 3 N 4 Gas can be released in the calcining process, so that the obtained catalyst has rich pore structure, and the requirements of electron conduction and mass transfer of reaction substances required by ORR are met; meanwhile, the higher specific surface area is beneficial to exposing a large number of metal active sites, and the utilization efficiency and ORR activity of the catalyst are improved.
(4) The ultra-high dispersion nanocluster structure Cu/NC catalyst prepared by the method has the advantages of low price of raw materials, low toxicity of reagents, wide raw material sources, economy, environmental protection, safe preparation process and good repeatability, and is beneficial to large-scale production of the catalyst. Compared with the commercialized ORR catalyst Pt/C, the catalyst has good stability and high activity, and can be used as a catalyst for a plurality of electrochemical devices such as fuel cells, metal-air batteries, water electrolysis devices and the like.
Drawings
FIG. 1 is a photograph of a spherical aberration correction electron microscope (STEM) of a sample prepared in example 3.
FIG. 2 (a) is a Transmission Electron Microscope (TEM) photograph and FIG. 2 (b) is a Scanning Electron Microscope (SEM) photograph of the sample obtained in example 3.
FIG. 3 (a) is a TEM photograph and FIG. 3 (b) is a SEM photograph of a sample obtained in comparative example 1.
FIG. 4 is a TEM photograph of a sample obtained in comparative example 2.
Fig. 5 is an X-ray diffraction (XRD) spectrum of the samples prepared according to example 3 and comparative example 1.
Fig. 6 (a) is a nitrogen adsorption and desorption curve of the samples prepared in example 3 and comparative example 2. FIG. 6 (b) is a graph showing pore size distribution curves of the samples of example 3 and comparative example 2
FIG. 7 shows a schematic view of a process according to examples 1 to 5The obtained sample was at room temperature O 2 Saturated 0.1moL L -1 ORR polarization curve in KOH electrolyte, rotational speed: 1600rpm, sweep rate: 10mV s -1 。
FIG. 8 is a graph of samples prepared according to example 3 and comparative examples 1 to 4 at room temperature O 2 Saturated 0.1moL L -1 ORR polarization curve in KOH electrolyte, rotational speed: 1600rpm, sweep rate: 10mV s -1 。
FIG. 9 (a) is a sample prepared according to example 3 at room temperature O 2 Saturated 0.1moL L -1 Linear Sweep Voltammetry (LSV) curve in KOH electrolyte, rotational speed: 400rpm, 625rpm, 900rpm, 1225rpm, 1600rpm, 2025rpm, and 2500rpm. FIG. 9 (b) is a Koutecky-Levich (K-L) plot at different potentials for the samples made according to example 3 of FIG. 9 (a).
FIG. 10 is a sample made according to example 3 versus comparative example 4 commercial 20wt.% Pt/C catalyst at room temperature with O 2 Saturated 0.1moL L -1 Chronoamperometry when the revolution rate in KOH electrolyte was 400rpm and the potential was constant at 0.57V.
Fig. 11 is an ORR polarization curve before and after 10000 cycles of accelerated aging test for the sample prepared according to example 3, rotation speed: 1600rpm, sweep rate: 10mV s -1 。
Detailed Description
The invention is described in detail below with reference to the drawings and specific examples.
Example 1: cu/NC 0.5g -800(NC 0.5g Adding g-C into raw materials 3 N 4 The mass of (3) was 0.5g,800 means that the calcination temperature was 800 ℃ C.)
0.5g of solid g-C are weighed 3 N 4 Adding 20mL of water, and ultrasonically dispersing for 30min. Adding copper nitrate trihydrate (72.5mg, 0.3mmol) and o-phenanthroline (178.4mg, 0.9mmol) into 15mL of water, and dissolving by ultrasonic for 30min. Then adding the mixed solution of copper nitrate and o-phenanthroline into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 3 ℃ for min -1 Is programmed to 800Calcining at constant temperature of 2 hr, etching the calcined material in 0.5M sulfuric acid solution at 50 deg.C, stirring for 5 hr, vacuum filtering, washing, and drying at 80 deg.C for 5 hr to obtain Cu/NC 0.5g 800 catalyst.
Example 2: cu/NC 1g -800(NC 1g Adding g-C into raw materials 3 N 4 The mass of (1) is 1g,800 means that the calcination temperature is 800 ℃ C.)
1g of solid g-C are weighed 3 N 4 Adding into 20mL water, and dispersing with ultrasound for 30min. Adding copper nitrate trihydrate (72.5 mg,0.3 mmol) and o-phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasonic wave for 30min. Then adding the mixed solution of copper nitrate and o-phenanthroline into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then putting the precursor solid material in N 2 At 3 ℃ for min -1 The temperature is programmed to 800 ℃ for calcination, the temperature is kept constant for 2h, finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain Cu/NC 1g 800 catalyst.
Example 3: cu/NC 2g -800(NC 2g Adding g-C into raw materials 3 N 4 Mass of (2 g), 800 means calcination temperature of 800 ℃)
2g of solid g-C are weighed 3 N 4 Adding 20mL of water, and ultrasonically dispersing for 30min. Adding copper nitrate trihydrate (72.5 mg,0.3 mmol) and o-phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasonic wave for 30min. Then adding the mixed solution of copper nitrate and phenanthroline into g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 3 deg.C for min -1 The temperature is programmed to 800 ℃ for calcination, the temperature is kept constant for 2h, finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain Cu/NC 2g -800 catalyst.
Example 4: cu/NC 3g -800(NC 3g Adding g-C into raw materials 3 N 4 Mass of (3 g,800 means calcination temperature of 800 ℃ C.)
3g of solid g-C are weighed 3 N 4 Adding 20mL of water, and ultrasonically dispersing for 30min. Adding copper nitrate trihydrate (72.5 mg,0.3 mmol) and phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasonic treatment for 30min. Then adding the mixed solution of copper nitrate and phenanthroline into g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then putting the precursor solid material in N 2 At 3 deg.C for min -1 The temperature is programmed to 800 ℃ for calcination, the temperature is kept constant for 2h, finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain Cu/NC 3g 800 catalyst.
Example 5: cu/NC 4g -800(NC 4g Adding g-C into raw materials 3 N 4 Having a mass of 4g,800 means a calcination temperature of 800 ℃)
4g of solid g-C are weighed 3 N 4 Adding into 20mL water, and dispersing with ultrasound for 30min. Adding copper nitrate trihydrate (72.5 mg,0.3 mmol) and phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasonic treatment for 30min. Then adding the mixed solution of copper nitrate and phenanthroline into g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 3 deg.C for min -1 Heating to 800 ℃ by program at the speed of (1) and calcining, keeping the temperature constant for 2h, finally etching and stirring the calcined material in 0.5M sulfuric acid solution at 50 ℃ for 5h, filtering, washing, and drying at 80 ℃ for 5h to obtain Cu/NC 4g -800 catalyst.
Example 6: cu/NC 2g -500(NC 2g Adding g-C into raw materials 3 N 4 Mass of (2 g,500 means calcination temperature of 500 ℃ C.)
2g of solid g-C are weighed 3 N 4 Adding into 20mL ethanol, and ultrasonically dispersing for 30min. Adding copper sulfate pentahydrate (74.9mg, 0.3mmol) and phenanthroline (5946.6mg, 30mmol) into 15mL of ethanol, and dissolving by ultrasonic treatment for 30min. However, the device is not limited to the specific type of the deviceThen adding the mixed solution of copper sulfate and phenanthroline into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then carrying out vacuum drying for 48 hours at 50 ℃ to obtain a precursor solid material. Then putting the precursor solid material in N 2 At 2 deg.C for min -1 Heating to 500 ℃ by speed program, calcining, keeping the temperature for 48h, etching the calcined material in 0.1M sulfuric acid solution at 120 ℃ for stirring for 1h, filtering, washing, and freeze-drying at-20 ℃ for 5h to obtain Cu/NC 2g -500 catalyst.
Example 7: cu/NC 2g -1100(NC 2g Adding g-C into raw materials 3 N 4 Mass of (2 g,1100 means calcination temperature of 1100 ℃ C.)
2g of solid g-C are weighed 3 N 4 Adding into 20mL of ethylene glycol, and ultrasonically dispersing for 30min. Copper chloride dihydrate (51.1mg, 0.3mmol) and 2,2' -bipyridine (4.7mg, 0.03mmol) were added to 15mL of ethylene glycol and dissolved by sonication for 30min. Then adding the mixed solution of copper chloride and 2,2' -bipyridyl into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 5 hours at 150 ℃ in an inert atmosphere to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 30 deg.C for min -1 The speed of the method is programmed to be heated to 1100 ℃ for calcination, the temperature is kept constant for 0.2h, finally, the calcined material is etched and stirred for 48h in 10M sulfuric acid solution at 50 ℃, filtered, washed and dried for 60h under the inert atmosphere at 300 ℃ to obtain Cu/NC 2g -1100 catalyst.
Example 8: cu/NC 2g -800(NC 2g Adding g-C into raw materials 3 N 4 Mass of (2 g), 800 means calcination temperature of 800 ℃)
2g of solid g-C are weighed 3 N 4 Adding into 20mL water, and dispersing with ultrasound for 30min. Copper nitrate trihydrate (72.5 mg,0.3 mmol) and ethylenediaminetetraacetic acid (263.0 mg,0.9 mmol) were added to 15mL of water and dissolved with sonication for 30min. Then adding the mixed solution of copper nitrate and ethylenediamine tetraacetic acid into the solution G-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then putting the precursor solid material in N 2 At 3 ℃ for min -1 The temperature is programmed to 800 ℃ for calcination, the temperature is kept constant for 2h, finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain Cu/NC 2g -800 catalyst.
Example 9: cu/NC 2g -800(NC 2g Adding g-C into raw materials 3 N 4 Mass of (2 g), 800 means calcination temperature of 800 ℃)
2g of solid g-C are weighed 3 N 4 Adding into 20mL water, and dispersing with ultrasound for 30min. Copper nitrate trihydrate (72.5 mg,0.3 mmol) and ethylenediamine (54.1mg, 0.9 mmol) were added to 15mL of water and dissolved by sonication for 30min. Then adding the mixed solution of copper nitrate and ethylenediamine into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then putting the precursor solid material in N 2 At 3 ℃ for min -1 The temperature is programmed to 800 ℃ for calcination at the constant temperature for 2h, and finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain Cu/NC 2g 800 catalyst.
Example 10: cu/NC 2g -800(NC 2g Adding g-C into raw materials 3 N 4 Mass of (2 g), 800 means calcination temperature of 800 ℃)
2g of solid g-C are weighed 3 N 4 Adding 20mL of water, and ultrasonically dispersing for 30min. Copper nitrate trihydrate (72.5 mg, 0.3mmol) and glycine (57.6 mg,0.9 mmol) were added to 15mL of water and dissolved by sonication for 30min. Then adding the mixed solution of copper nitrate and glycine into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 3 deg.C for min -1 The temperature is programmed to 800 ℃ for calcination at the constant temperature for 2h, and finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain Cu/NC 2g -800 catalyst.
Comparative example 1: cu/NC 2g -800-A(NC 2g Adding g-C into raw materials 3 N 4 The mass of (A) is 2g, the calcination temperature is 800 ℃ and A is etching without using sulfuric acid after the calcination is finished)
2g of solid g-C are weighed 3 N 4 Adding into 20mL water, and dispersing with ultrasound for 30min. Adding copper nitrate trihydrate (72.5 mg,0.3 mmol) and phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasonic treatment for 30min. Then adding the mixed solution of copper nitrate and phenanthroline into g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then putting the precursor solid material in N 2 At 3 deg.C for min -1 The temperature is increased to 800 ℃ by the speed program, the calcination is carried out, the constant temperature is kept for 2 hours, and the Cu/NC is obtained 2g -800-a catalyst.
Comparative example 2: cu/NC 2g -800-B(NC 2g Adding g-C into raw materials 3 N 4 The mass of (B) is 2g, the calcination temperature is 800 ℃, the B is nitric acid treatment after the preparation is finished
2g of solid g-C are weighed 3 N 4 Adding into 20mL water, and dispersing with ultrasound for 30min. Adding copper nitrate trihydrate (72.5 mg,0.3 mmol) and o-phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasonic wave for 30min. Then adding the mixed solution of copper nitrate and o-phenanthroline into the g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 3 ℃ for min -1 Heating to 800 ℃ by program at the speed of (1) and calcining, keeping the temperature constant for 2h, finally etching and stirring the calcined material in 0.5M sulfuric acid solution at 50 ℃ for 5h, filtering, washing, and drying at 80 ℃ for 5h to obtain Cu/NC 2g -800 catalyst.
Mixing Cu/NC 2g Etching and stirring a-800 catalyst in 1M nitric acid solution at 60 ℃ for 5h, performing suction filtration, washing, and drying at 80 ℃ for 5h to obtain Cu/NC 2g -800-B catalyst
Comparative example 3: NC (numerical control) 2g -800(NC 2g Adding g-C into raw materials 3 N 4 The mass of (1) is 2g, no copper nitrate is added in the preparation process, 800 refers to calcinationThe burning temperature is 800℃)
2g of solid g-C are weighed 3 N 4 Adding 20mL of water, and ultrasonically dispersing for 30min. Adding phenanthroline (178.4 mg,0.9 mmol) into 15mL of water, and dissolving by ultrasound for 30min. Then adding phenanthroline solution into g-C 3 N 4 And uniformly stirring the dispersion liquid for 12 hours at room temperature, and then drying the dispersion liquid for 10 hours at 80 ℃ to obtain a precursor solid material. Then adding the precursor solid material into N 2 At 3 ℃ for min -1 The temperature is programmed to 800 ℃ for calcination, the temperature is kept constant for 2h, finally the calcined material is etched and stirred for 5h in 0.5M sulfuric acid solution at 50 ℃, filtered, washed and dried for 5h at 80 ℃ to obtain NC 2g 800 catalyst.
Comparative example 4 commercial 20wt.% Pt/C catalyst
FIG. 1 is a photograph of a spherical aberration correction electron microscope (STEM) of a sample prepared in example 3. In the figure, the white particles are copper nano particle clusters, and the copper nano particle clusters are uniformly dispersed on the graphite carbon layer, are regular in appearance and have the particle size of about 2-3 nm;
FIG. 2 (a) is a Transmission Electron Microscope (TEM) photograph of the sample obtained in example 3, and FIG. 2 (b) is a Scanning Electron Microscope (SEM) photograph of the sample obtained in example 3. It can be seen from the figure that the catalyst forms a graphene sheet layer structure, has a large specific surface area, is beneficial to exposing more active sites, and has no copper particles with a large particle size on the surface, because the copper particles on the surface of the material are removed by using sulfuric acid etching after the calcination is completed.
FIG. 3 (a) is a TEM photograph and FIG. 3 (b) is a SEM photograph of a sample obtained in comparative example 1. It can be seen that the catalyst formed a graphene lamellar structure, similar to that of example 3, but formed larger copper particles at the surface.
FIG. 4 is a TEM photograph of a sample obtained in comparative example 2. The appearance of the graphene lamellar structure formed by the photo-visible catalyst is similar to that of the sample prepared in example 3, which shows that the appearance of the sample is not greatly changed after the sample is treated by nitric acid.
Fig. 5 is an X-ray diffraction (XRD) spectrum of the samples prepared according to example 3 and comparative example 1. As can be seen from fig. 5, the sample obtained in comparative example 1 showed characteristic peaks (PCPDF #85 to 1326) in the Cu (111), cu (200) and Cu (220) crystal planes at 43.3 °, 50.4 ° and 74.1 °, respectively, indicating that Cu nanoparticles having a larger particle size were present in comparative example 1, which is consistent with the TEM observation result in fig. 2. In example 3, the sample is prepared after being etched by sulfuric acid, and XRD results show that no characteristic peak of strong Cu crystals appears in example 3, which indicates that large Cu nanoparticles on the surface of the catalyst are removed after being etched by sulfuric acid.
FIG. 6 (a) is a graph showing the nitrogen adsorption and desorption curves of the samples prepared in example 3 and comparative example 2, and it can be seen from FIG. 6 (a) that the relative pressure P/P is measured 0 At 0.8, hysteresis loops (adsorption type IV) appeared in both samples, indicating that these materials are both mesoporous materials; FIG. 6 (b) is the pore size distribution curves of the samples of example 3 and comparative example 2, and it can be seen from the graph that the pore size ranges of the two samples are mainly distributed between 3nm and 4nm and between 15 nm and 64nm, and the hierarchical pore structure can sufficiently meet the mass transfer requirement of ORR. In addition, comparative example 2 showed a pore structure in the range of 2 to 3nm, indicating that nitric acid may etch away part of the Cu nanoclusters located at the surface of the material, which also resulted in the BET specific surface area (269.6 m) of comparative example 2 2 g -1 ) Greater than example 3 (254.4 m) 2 g -1 )。
FIG. 7 is a graph of samples prepared according to examples 1-5 at room temperature O 2 Saturated 0.1moL L -1 ORR polarization curve in KOH electrolyte, rotational speed: 1600rpm, sweep rate: 10mV s -1 . As can be seen from FIG. 7, the catalyst obtained in example 3 had an initial potential E onset ＝E (j＝-0.1mAcm -2 ) And half-wave potential E 1/2 ＝E (j＝-3mAcm -2 ) The highest indicates that it has good ORR activity. With addition of g-C 3 N 4 The amount of ORR increases from 0.5g to 4g, the ORR initial potential and the limiting current density of each example increase and then decrease, when g-C is added 3 N 4 The maximum limiting current density and half-wave potential were the highest at an amount of 2g, and the catalyst exhibited the highest activity.
FIG. 8 is a graph of samples prepared according to example 3 and comparative examples 1 to 4 at room temperature O 2 Saturated 0.1moL L -1 ORR polarization curve in KOH electrolyteSpeed: 1600rpm, sweep rate: 10mV s -1 . As can be seen from FIG. 8, the initial potential E of the sample not subjected to sulfuric acid etching (comparative example 1) is higher than that of the sample subjected to sulfuric acid etching (example 3) onset And half-wave potential E 1/2 This approach indicates that the sulfuric acid etch did not alter the activity of the catalyst, a result which indicates that the large particles of copper present on the surface of the material prior to the sulfuric acid etch were not catalytically active. In addition, the initial potential E of the sample after nitric acid etching (comparative example 2) is higher than that of the sample without nitric acid etching (example 3) onset And half-wave potential E 1/2 The limiting current is relatively poor, and analysis of nitrogen adsorption and desorption results shows that part of the Cu nanoclusters can be etched after nitric acid etching, which indicates that the Cu nanoclusters are beneficial to the ORR process.
FIG. 9 (a) is a sample prepared according to example 3 at room temperature O 2 Saturated 0.1moL L -1 Linear Sweep Voltammetry (LSV) curve in KOH electrolyte, rotational speed: 400rpm, 625rpm, 900rpm, 1225rpm, 1600rpm, 2025rpm and 2500rpm. As can be seen from fig. 9 (a), as the rotation speed increases, the ORR initial potential remains constant, and the limiting diffusion current density increases. FIG. 9 (b) is a Koutecky-Levich (K-L) plot at different potentials for the samples made according to example 3 of FIG. 9 (a). The electron transfer number calculated according to the K-L equation is about 4.05, which shows that the catalyst mainly catalyzes ORR in a high-efficiency 4-electron process and has very high catalytic selectivity.
FIG. 10 is a plot of the sample made according to example 3 versus a commercial 20wt.% Pt/C catalyst of comparative example 4 at room temperature, O 2 Saturated 0.1moL L -1 Chronoamperometry when the revolution rate in KOH electrolytic solution was 400rpm and the potential was constant at 0.57V. By comparison, the activity of the catalyst prepared in example 3 decays to 87% after the stability test of chronoamperometry current of 10000 s; under the same conditions, the activity decay of the commercial 20wt.% Pt/C catalyst after 1800s has reached 83%, indicating that the catalyst prepared in example 3 has better stability than the commercial Pt/C.
FIG. 11 is an ORR polarization curve before and after 10000 cycles of accelerated aging test of samples prepared according to example 3, rotation speed: 1600rpm, sweep rate: 10mV s -1 . By comparing the ORR curves before and after 10000 cycles of cyclic scan, it can be seen that the two curves are approximately coincident, indicating that the catalyst prepared in example 3 has very excellent cyclic stability.

Claims (8)

1. The preparation method of the high-dispersion Cu/NC nano-cluster catalyst is characterized in that the nano-cluster catalyst is g-C which is cheap and easy to obtain 3 N 4 The preparation method comprises the following steps of mixing an organic ligand as a metal complex and a metal copper salt as a Cu precursor as a carrier, calcining at a high temperature, and performing appropriate post-treatment to obtain the Cu/NC electrocatalyst containing the highly dispersed Cu nanoclusters:
in the first step, the g-C is treated by a microwave method and a heat treatment method 3 N 4 Precursor, preparation of g-C 3 N 4 (ii) a G to C 3 N 4 Adding into solvent for dispersion to obtain g-C 3 N 4 A dispersion liquid;
secondly, adding copper salt and organic ligand into a solvent to obtain a mixed solution, and adding the mixed solution into g-C 3 N 4 Drying the dispersion liquid to obtain a precursor solid material; the molar ratio of the copper salt to the organic ligand is 1.1-100;
and thirdly, calcining the precursor solid material in an inert atmosphere, raising the temperature to 500-1100 ℃ by room temperature programming, carrying out constant temperature treatment for 0.2-48 h, carrying out etching treatment on the calcined material in an acid solution, washing and drying to obtain the target catalyst.
2. The process according to claim 1, wherein g-C is used in the first step 3 N 4 The precursor is one or more of melamine, urea and dicyanodiamine.
3. The method according to claim 1, wherein the organic ligand in the second step is one or more selected from the group consisting of phenanthroline, 2' -bipyridine, ethylenediamine tetraacetic acid, ethylenediamine, and glycine.
4. The method of claim 1, wherein the copper salt is one or more of copper nitrate, copper sulfate, and copper chloride.
5. The preparation method according to claim 1, wherein the acid solution used for etching in the third step is one or more of sulfuric acid, hydrochloric acid and nitric acid; the concentration of the acid solution is 0.1-10 mol L -1 The etching time is 1-48 h, and the etching temperature is 50-120 ℃.
6. The preparation method according to claim 1, wherein the first step solvent is one or more of water, ethanol and ethylene glycol; in the second step, the solvent is one or more of water, ethanol and glycol.
7. The method according to claim 1, wherein the drying method in the second step is vacuum drying, air atmosphere drying, inert atmosphere drying, the drying temperature is 50-150 ℃, and the drying time is 5-48 h.
8. The preparation method of claim 1, wherein the drying method in the third step is vacuum drying, air atmosphere drying, inert atmosphere drying, or freeze drying, the drying temperature is-20 to 300 ℃, and the drying time is 5 to 60 hours.
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