CN111437864B - A kind of highly dispersed Cu/NC nano-cluster catalyst and its preparation method - Google Patents

Abstract

A highly dispersed Cu/NC nano-cluster catalyst and a preparation method thereof belong to the field of energy materials and electrochemical technology. The nano-cluster catalyst uses cheap and easy-to-obtain g-C ₃ N ₄ as a carrier, an organic ligand as a metal complex, and a metal copper salt as a Cu precursor. After 0.2-48h, the calcined material is etched in an acidic solution, washed and dried to obtain a Cu/NC electrocatalyst containing highly dispersed Cu nanoclusters. By adjusting the ratio of Cu precursor, g-C ₃ N ₄ and organic ligands, as well as the calcination temperature and time, the morphology and pore structure of the catalyst can be controlled, and a catalyst with excellent ORR performance can be optimized. The preparation method of the invention is simple, the raw material price is low, the prepared catalyst has good stability and high activity, and can realize large-scale production.

Description

A kind of highly dispersed Cu/NC nano-cluster catalyst and its preparation method

technical field

The invention belongs to the technical field of energy materials and electrochemistry, and relates to a cathode oxygen reduction reaction electrocatalyst, in particular to a highly dispersed Cu/NC nano-cluster structure catalyst and a preparation method thereof.

Background technique

Fuel cell is a research focus of domestic and foreign scholars in recent years. However, the core challenge of the cathode oxygen reduction reaction (ORR) in fuel cells is the slow kinetic process. At present, the best performance and most widely used fuel cell ORR catalysts are Pt-based catalysts, but Pt-based catalysts are poor in stability, high in price and have limited Pt reserves, which limit the large-scale commercial use of fuel cells, so the development of catalysts with high catalytic Active and stable, corrosion-resistant, low-cost catalysts have important practical significance and application value.

Among several earth-abundant transition metals, copper-based materials have attracted much attention due to 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 copper nanoparticles. For example, Kang et al. [Journal of Alloys and Compounds, 2019, 795, 462-470] reported that Cu and Co bimetallic intercalated nitrogen-doped carbons can serve as efficient ORR electrocatalysts, in which Cu precursors were incorporated into Co-based zeolite imidazolates. Among the framework precursors, not only the activity of Co can be enhanced synergistically, but also the nitrogen content in the catalyst can be increased, which can generate more active sites and thus enhance the ORR activity. However, its stability and activity still need to be greatly improved to meet the practical application.

In order to achieve high-efficiency catalysis, preparing materials into ultra-highly dispersed nanocluster catalysts is one of the most direct and effective strategies. Nanoclusters refer to ultra-small metal nanoparticles aggregated from a few to hundreds of metal atoms, with a particle size of about 2nm. The size effect makes this type of material have special "molecular-like properties". For example, Zou et al. [Adv.Mater.2017,29,1606200] reported an electrode material based on copper foam as a carrier, subnanometer copper clusters and quasi-amorphous metal sulfide, and found that it has both efficient hydrogen evolution and Oxygen catalytic activity. They believe that in addition to the catalytic activity of the quasi-amorphous metal sulfide itself, the subnanometer copper clusters can effectively induce the redistribution of the surface charge of the material, and at the same time promote the dissociation and adsorption of water molecules on the surface of the material during the catalytic process. This is the first report on the facilitation of subnanometer copper clusters for water splitting reactions. However, to the best of our knowledge, copper nanoclusters have not been reported to catalyze ORR.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention designs and prepares a Cu/NC electrocatalyst with a highly dispersed nano-cluster structure and a preparation method thereof. In the present invention, the organic ligand is used to complex metal copper, which is beneficial to prevent metal copper from agglomerating, so that a Cu nano-cluster structure is formed on the surface of the catalyst. The use of porous gC ₃ N ₄ as a carrier is beneficial to increase the specific surface area of the catalyst, enrich the pore structure of the catalyst, and expose more active sites. In addition, the higher content of N in gC ₃ N ₄ makes the catalyst produce more Multiple defective active sites. Therefore, the catalyst prepared by the present invention is a porous Cu/NC nano-cluster catalyst with high active site density. The preparation method of the catalyst is simple and the cost is low, and it can be put into industrial production as an excellent substitute of the noble metal Pt-based catalyst.

In order to achieve the above object, the concrete technical scheme that the present invention adopts is as follows:

A highly dispersed Cu/NC nano-cluster catalyst, the nano-cluster catalyst uses cheap and easy-to _- obtain _gC3N4 as a carrier, an organic ligand as a metal complex, and a metal copper salt as a Cu precursor. High-temperature calcination and appropriate post-treatment yielded Cu/NC electrocatalysts containing highly dispersed Cu nanoclusters. By adjusting the ratio of Cu precursor, gC ₃ N ₄ and organic ligands, as well as the calcination temperature and time, the morphology and pore structure of the catalyst can be controlled, and a catalyst with excellent ORR performance can be optimized.

A preparation method of highly dispersed Cu/NC nano-cluster catalyst, comprising steps as follows:

In the first step, the gC ₃ N ₄ precursor is treated with a microwave method and a heat treatment method to prepare gC ₃ N ₄ ; gC ₃ N ₄ is added into a solvent for dispersion to obtain a gC ₃ N ₄ dispersion.

In the second step, the copper salt and the organic ligand are added to the solvent to obtain a mixed solution, and then the mixed solution is added to the gC ₃ N ₄ dispersion, and dried to obtain a precursor solid material. The molar ratio of the copper salt to the organic ligand is 1:0.1-100.

The third step is to calcinate the precursor solid material in an inert atmosphere, heat up to a calcination temperature of 500-1100° C. at room temperature, and perform a constant temperature treatment for 0.2-48 hours. The calcined material is etched in an acidic solution, washed and After drying, the target catalyst was obtained.

In the first step, the gC ₃ N ₄ precursor is one or more of melamine, urea, and dicyandiamide.

In the second step, the organic ligand is one or more Cu ligands such as o-phenanthroline, 2,2'-bipyridine, ethylenediaminetetraacetic acid, ethylenediamine, and glycine. The copper salt is one or more of copper nitrate, copper sulfate and copper chloride.

The solvent in the first step is one or more of water, ethanol, ethylene glycol, etc.; the solvent in the second step is one or more of water, ethanol, ethylene glycol, etc.

The drying method in the second step is vacuum drying, air atmosphere drying, and inert atmosphere drying, the drying temperature is 50-150° C., and the drying time is 5-48 hours.

The temperature programming rate of calcination in the third step is 2-30°C min ^-1 .

The acidic solution used for etching in the third step is one or more of acids such as sulfuric acid, hydrochloric acid, and nitric acid. The concentration of the acidic solution is 0.1-10mol L ^-1 , the etching time is 1-48h, and the etching temperature is 50-120°C.

The drying method in the third step is vacuum drying, air atmosphere drying, inert atmosphere drying, freeze drying, the drying temperature is -20-300° C., and the drying time is 5-60 hours.

Compared with the prior art, the Cu/NC catalyst with ultra-high dispersion nano-cluster structure and preparation method of the present invention have the following advantages:

(1) Adopt the ultra-high dispersion nano-cluster structure Cu/NC catalyst prepared by the method of the present invention, used gC ₃ N ₄ not only make carbon source but also make nitrogen source, help to improve the nitrogen content in the catalyzer, help to improve ORR reactivity. The two-dimensional planar gC ₃ N ₄ can be aggregated to form graphene-like sheets during the calcination process, which has a large specific surface area and high conductivity, which can meet the requirements of mass transfer and conductivity of the material and ensure the catalytic performance of the material.

(2) The ultra-high dispersion nanocluster structure Cu/NC catalyst prepared by the method of the present invention can promote copper ions to be complexed and evenly anchored in gC by adding organic ligands as complexes of metal copper ions In the ₃ N ₄ layer, metal particles can be effectively prevented from agglomerating during the calcination process, so that the distribution of active-site metal nanoparticles in the catalyst is more uniform and the nanoparticles are smaller, thereby improving the activity and stability of the catalyst.

(3) Using the ultra-highly dispersed nano-cluster structure Cu/NC catalyst prepared by the method of the present invention, gC ₃ N ₄ can release gas during the calcination process, so that the obtained catalyst has a rich pore structure, which is conducive to satisfying the ORR The required electronic conduction and reaction mass transfer requirements; at the same time, the higher specific surface area is conducive to exposing a large number of metal active sites, improving catalyst utilization efficiency and ORR activity.

(4) Adopt the ultra-high dispersion nano-cluster structure Cu/NC catalyst prepared by the method of the present invention, the raw material used is cheap, reagent toxicity is little, raw material source is extensive, economical and environmental protection, preparation process safety, repeatability are good, be conducive to The catalyst achieves large-scale production. Compared with the commercial ORR catalyst Pt/C, it has good stability and high activity, and can be used as a catalyst for multiple electrochemical devices such as fuel cells, metal-air batteries, and electrolytic water devices.

Description of drawings

Fig. 1 is the spherical aberration-corrected electron microscope (STEM) photo of the sample prepared in Example 3.

Fig. 2 (a) is the transmission electron microscope (TEM) photograph of the sample prepared in embodiment 3, and Fig. 2 (b) is the scanning electron microscope (SEM) photograph of the sample obtained in embodiment 3.

FIG. 3( a ) is a TEM photo of the sample prepared in Comparative Example 1, and FIG. 3( b ) is a SEM photo of the sample prepared in Comparative Example 1.

Fig. 4 is the TEM photo of the sample prepared in Comparative Example 2.

5 is an X-ray diffraction (XRD) spectrum of samples prepared according to Example 3 and Comparative Example 1.

Figure 6(a) is the nitrogen adsorption and desorption curves of the samples prepared in Example 3 and Comparative Example 2. Fig. 6 (b) is the pore size distribution curve of embodiment 3 and comparative example 2 samples

Fig. 7 shows the ORR polarization curves of samples prepared according to Examples 1-5 in 0.1moL L ^-1 KOH electrolyte saturated with O ₂ at room temperature, rotation speed: 1600 rpm, scan rate: 10 mV s ^-1 .

Figure 8 shows the ORR polarization curves of the samples prepared according to Example 3 and Comparative Examples 1-4 in 0.1moL L ^-1 KOH electrolyte saturated with O ₂ at room temperature, rotation speed: 1600rpm, scan rate: 10mV s ^-1 .

Figure 9(a) is the linear sweep voltammetry (LSV) curve of the sample prepared according to Example 3 at room temperature in a 0.1moL L ^-1 KOH electrolyte saturated with O ₂ . 1600rpm, 2025rpm and 2500rpm. Fig. 9(b) is the Koutecky-Levich (KL) curves of the samples prepared according to Example 3 in Fig. 9(a) at different potentials.

Figure 10 shows the samples prepared according to Example 3 and the commercialized 20wt.% Pt/C catalyst of Comparative Example 4 at room temperature, O ₂ saturated 0.1moL L ^-1 KOH electrolyte with a rotation speed of 400rpm and a constant potential at 0.57V chronocurrent diagram.

Fig. 11 shows the ORR polarization curves of the sample prepared according to Example 3 before and after 10,000 cycles of the accelerated aging test cycle, the rotational speed: 1600 rpm, and the sweep rate: 10 mV s ^-1 .

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific examples.

Example 1: Cu/NC _0.5g -800 (NC _0.5g means the mass of gC ₃ N ₄ added to the raw material is 0.5g, 800 means the calcination temperature is 800°C)

Weigh 0.5g of solid gC ₃ N ₄ into 20mL of water, and ultrasonically disperse for 30min. Add copper nitrate trihydrate (72.5mg, 0.3mmol) and o-phenanthroline (178.4mg, 0.9mmol) into 15mL of water, and dissolve by ultrasonication for 30min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _0.5g -800 catalyst.

Example 2: Cu/NC _1g -800 (NC _1g means that the mass of gC ₃ N ₄ added to the raw material is 1g, and 800 means that the calcination temperature is 800°C)

Weigh 1 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _1g -800 catalyst.

Example 3: Cu/NC _2g -800 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, and 800 means that the calcination temperature is 800°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _2g -800 catalyst.

Example 4: Cu/NC _3g -800 (NC _3g means that the mass of gC ₃ N ₄ added to the raw material is 3g, and 800 means that the calcination temperature is 800°C)

Weigh 3 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _3g -800 catalyst.

Example 5: Cu/NC _4g -800 (NC _4g means that the mass of gC ₃ N ₄ added to the raw material is 4g, and 800 means that the calcination temperature is 800°C)

Weigh 4 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _4g -800 catalyst.

Example 6: Cu/NC _2g -500 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, and 500 means that the calcination temperature is 500°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of ethanol, and ultrasonically disperse for 30 min. Add copper sulfate pentahydrate (74.9 mg, 0.3 mmol) and o-phenanthroline (5946.6 mg, 30 mmol) into 15 mL of ethanol, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper sulfate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 hours, and then vacuum-dried at 50° C. for 48 hours to obtain a solid precursor material. Then the precursor solid material was heated to 500°C in N ₂ at a rate of 2°C min ^-1 for calcination, and the temperature was maintained for 48h. Finally, the calcined material was etched and stirred in 0.1M sulfuric acid solution at 120°C for 1h, pumped Filter, wash, and freeze-dry at -20°C for 5 hours to obtain Cu/NC _2g -500 catalyst.

Example 7: Cu/NC _2g -1100 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, and 1100 means that the calcination temperature is 1100°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of ethylene glycol, and ultrasonically disperse for 30 min. Add copper chloride dihydrate (51.1mg, 0.3mmol) and 2,2'-bipyridine (4.7mg, 0.03mmol) into 15mL of ethylene glycol, and dissolve by ultrasonication for 30min. Then, the mixed solution of copper chloride and 2,2'-bipyridyl was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 hours, and then dried in an inert atmosphere at 150° C. for 5 hours to obtain a solid precursor material. Then the precursor solid material was heated to 1100°C in _N2 at a rate of 30°C min ^-1 for calcination, and the temperature was kept constant for 0.2h. Finally, the calcined material was etched and stirred in 10M sulfuric acid solution at 50°C for 48h, pumped Filter, wash, and dry in an inert atmosphere at 300°C for 60 hours to obtain a Cu/NC _2g -1100 catalyst.

Example 8: Cu/NC _2g -800 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, and 800 means that the calcination temperature is 800°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and ethylenediaminetetraacetic acid (263.0 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and ethylenediaminetetraacetic acid was added to the gC ₃ N ₄ dispersion liquid, uniformly stirred at room temperature for 12 hours, and then dried at 80° C. for 10 hours to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _2g -800 catalyst.

Example 9: Cu/NC _2g -800 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, and 800 means that the calcination temperature is 800°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and ethylenediamine (54.1 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and ethylenediamine was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a precursor solid material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _2g -800 catalyst.

Example 10: Cu/NC _2g -800 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, and 800 means that the calcination temperature is 800°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and glycine (57.6 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and glycine was added into the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a precursor solid material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _2g -800 catalyst.

Comparative example 1: Cu/NC _2g -800-A (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, 800 means that the calcination temperature is 800°C, and A means that sulfuric acid is not used for etching after calcination)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was calcined in N ₂ at a rate of 3°C min ^-1 at a rate of 3°C min -1 to 800°C for calcination, and the temperature was kept constant for 2h to obtain Cu/NC _2g -800-A catalyst.

Comparative example 2: Cu/NC _2g -800-B (NC _2g refers to the mass of gC ₃ N ₄ added to the raw material is 2g, 800 refers to the calcination temperature of 800°C, B refers to nitric acid treatment after preparation)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add copper nitrate trihydrate (72.5 mg, 0.3 mmol) and o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water, and dissolve by ultrasonication for 30 min. Then, the mixed solution of copper nitrate and o-phenanthroline was added to the gC ₃ N ₄ dispersion, uniformly stirred at room temperature for 12 h, and then dried at 80° C. for 10 h to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was kept constant for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h, pumped Filter, wash, and dry at 80°C for 5 hours to obtain Cu/NC _2g -800 catalyst.

The Cu/NC _2g -800 catalyst was etched and stirred in 1M nitric acid solution at 60°C for 5h, suction filtered, washed, and dried at 80°C for 5h to obtain the Cu/NC _2g -800-B catalyst

Comparative example 3: NC _2g -800 (NC _2g means that the mass of gC ₃ N ₄ added to the raw material is 2g, no copper nitrate is added in the preparation process, 800 means the calcination temperature is 800°C)

Weigh 2 g of solid gC ₃ N ₄ into 20 mL of water, and ultrasonically disperse for 30 min. Add o-phenanthroline (178.4 mg, 0.9 mmol) into 15 mL of water and dissolve it by ultrasonication for 30 min. Then the o-phenanthroline solution was added to the gC ₃ N ₄ dispersion, stirred evenly at room temperature for 12 hours, and then dried at 80° C. for 10 hours to obtain a solid precursor material. Then the precursor solid material was heated to 800°C in _N2 at a rate of 3°C min ^-1 for calcination, and the temperature was maintained for 2h. Finally, the calcined material was etched and stirred in 0.5M sulfuric acid solution at 50°C for 5h. Suction filtration, washing, and drying at 80°C for 5 hours gave NC _2g -800 catalyst.

Comparative example 4 commercialization 20wt.%Pt/C catalyst

Fig. 1 is the spherical aberration-corrected electron microscope (STEM) photo of the sample prepared in Example 3. The white particles in the figure are clusters of copper nanoparticles. It can be seen from the figure that the copper nanoclusters are evenly dispersed on the graphite carbon layer, with regular appearance and a particle size of about 2-3nm;

Fig. 2 (a) is the transmission electron microscope (TEM) photograph of the sample prepared in embodiment 3, and Fig. 2 (b) is the scanning electron microscope (SEM) photograph of the sample obtained in embodiment 3. It can be seen from the figure that the catalyst forms a graphene sheet structure, which has a larger specific surface area, which is conducive to exposing more active sites, and there are no large-sized copper particles on the surface, which is due to the use of sulfuric acid etching after calcination. Copper particles on the surface of the material are removed.

FIG. 3( a ) is a TEM photo of the sample prepared in Comparative Example 1, and FIG. 3( b ) is a SEM photo of the sample prepared in Comparative Example 1. It can be seen from the figure that the catalyst forms a graphene sheet structure, which is similar to the structure of Example 3, but larger copper particles are formed on the surface.

Fig. 4 is the TEM photo of the sample prepared in Comparative Example 2. It can be seen from the photo that the catalyst forms a graphene sheet structure, which is similar to the morphology of the sample prepared in Example 3, indicating that the morphology of the sample does not change significantly after being treated with nitric acid.

5 is an X-ray diffraction (XRD) spectrum of samples prepared according to Example 3 and Comparative Example 1. As can be seen from Figure 5, the samples prepared in Comparative Example 1 appear at 43.3 °, 50.4 ° and 74.1 °, respectively, the characteristic peaks of Cu(111), Cu(200) and Cu(220) crystal planes (PCPDF#85-1326), It shows that Cu nanoparticles with larger particle size exist in Comparative Example 1, which is consistent with the TEM observation results in FIG. 2 . Example 3 is a sample obtained after sulfuric acid etching, and the XRD results show that there is no characteristic peak of strong Cu crystals in Example 3, indicating that after sulfuric acid etching, the larger Cu nanoparticles on the catalyst surface are remove.

Figure 6(a) is the nitrogen adsorption-desorption curves of the samples prepared in Example 3 and Comparative Example 2. It can be found from Figure 6(a) that when the relative pressure P/P ₀ is 0.8, hysteresis loops appear in both samples (adsorption type IV), illustrating that these materials are all mesoporous materials; Fig. 6 (b) is the pore size distribution curve of embodiment 3 and comparative example 2 samples, as seen from the figure, the pore size range of two samples is mainly distributed in 3～4nm and 15-64nm, its hierarchical pore structure can fully meet the mass transfer requirements of ORR. In addition, comparative example 2 has a pore structure in the range of 2-3nm, indicating that nitric acid may etch away part of the Cu nanoclusters located on the surface of the material. This result also leads to the BET specific surface area of comparative example 2 (269.6m ² g ^-1 ) It is larger than Example 3 (254.4m ² g ^-1 ).

Fig. 7 shows the ORR polarization curves of samples prepared according to Examples 1-5 in 0.1moL L ^-1 KOH electrolyte saturated with O ₂ at room temperature, rotation speed: 1600 rpm, scan rate: 10 mV s ^-1 . It can be seen from Figure 7 that the onset potential E _onset =E _(j=-0.1mAcm ^-2 ₎ and the half-wave potential E _1/2 =E _(j=-3mAcm ^-2 ₎ of the catalyst prepared in Example 3 are the highest, indicating that its Has good ORR activity. As the amount of gC ₃ N ₄ added increases from 0.5g to 4g, the ORR onset potential and limiting current density of each example increase first and then decrease. When the amount of gC ₃ N ₄ added is 2g, the limiting current density and half The wave potential is the highest, and the catalyst exhibits the highest activity.

Figure 8 shows the ORR polarization curves of the samples prepared according to Example 3 and Comparative Examples 1-4 in 0.1moL L ^-1 KOH electrolyte saturated with O ₂ at room temperature, rotation speed: 1600rpm, scan rate: 10mV s ^-1 . As can be seen from Figure 8, compared with the sample etched by sulfuric acid (comparative example 1) and the sample etched by sulfuric acid (example 3), the onset potential E _onset and the half-wave potential E _1/2 are close, indicating that sulfuric acid etched Etching did not change the activity of the catalyst. This result indicates that the large particles of copper present on the surface of the material before sulfuric acid etching have no catalytic activity. In addition, compared with the sample (Example 3) after nitric acid etching, the onset potential E _onset and the half-wave potential E _1/2 of Comparative Example 2 and the limiting current Both are relatively poor, combined with the analysis of nitrogen adsorption and desorption results, it can be seen that after nitric acid etching, some Cu nanoclusters may also be etched away, indicating that Cu nanoclusters are beneficial to the ORR process.

Figure 9(a) is the linear sweep voltammetry (LSV) curve of the sample prepared according to Example 3 at room temperature in a 0.1moL L ^-1 KOH electrolyte saturated with O ₂ . 1600rpm, 2025rpm and 2500rpm. It can be seen from Figure 9(a) that as the rotation speed increases, the ORR onset potential remains unchanged, and the limiting diffusion current density increases continuously. Fig. 9(b) is the Koutecky-Levich (KL) curves of the samples prepared according to Example 3 in Fig. 9(a) at different potentials. According to the KL equation, the electron transfer number is calculated to be around 4.05, indicating that the catalyst mainly catalyzes ORR with an efficient 4-electron process, and the catalytic selectivity is very high.

Figure 10 shows the samples prepared according to Example 3 and the commercialized 20wt.% Pt/C catalyst of Comparative Example 4 at room temperature, O ₂ saturated 0.1moL L ^-1 KOH electrolyte with a rotation speed of 400rpm and a constant potential at 0.57V chronocurrent diagram. By comparison, it can be seen that after the chronoamperometric stability test of 10000s, the activity of the catalyst prepared in Example 3 decayed to 87%; under the same conditions, the activity of the commercialized 20wt.%Pt/C catalyst decayed to 83% after 1800s , indicating that the stability of the catalyst prepared in Example 3 is better than that of commercial Pt/C.

Fig. 11 shows the ORR polarization curves of the sample prepared according to Example 3 before and after 10,000 cycles of the accelerated aging test cycle, the rotational speed: 1600 rpm, and the sweep rate: 10 mV s ^-1 . By comparing the ORR curves before and after 10,000 cycle scans, it can be seen that the two curves are close to overlapping, indicating that the catalyst prepared in Example 3 has very excellent cycle stability.

Claims (8)

1. A preparation method for a highly dispersed Cu/NC nano-cluster catalyst, characterized in that the nano-cluster catalyst is cheap and easy to get gC ₃ N ₄ as a carrier, with an organic ligand as a metal complex, and with metal copper The salt is used as a Cu precursor, and after being mixed, it is calcined at a high temperature and appropriately post-treated to obtain a Cu/NC electrocatalyst containing highly dispersed Cu nanoclusters. The steps of the preparation method are as follows: In the first step, the gC ₃ N ₄ precursor is treated by microwave method and heat treatment method to prepare gC ₃ N ₄ ; gC ₃ N ₄ is added into a solvent for dispersion to obtain a gC ₃ N ₄ dispersion; In the second step, the copper salt and the organic ligand are added to the solvent to obtain a mixed solution, and then the mixed solution is added to the gC ₃ N ₄ dispersion, and dried to obtain a precursor solid material; the molar ratio of the copper salt and the organic ligand is: 1:0.1～100; The third step is to calcinate the precursor solid material in an inert atmosphere, heat up to a calcination temperature of 500-1100° C. at room temperature, and perform a constant temperature treatment for 0.2-48 hours. The calcined material is etched in an acidic solution, washed and After drying, the target catalyst was obtained. 2. The preparation method according to claim 1, characterized in that the gC ₃ N ₄ precursor in the first step is one or more of melamine, urea, and dicyandiamide. 3. preparation method according to claim 1, is characterized in that, in the described second step, organic ligand is o-phenanthroline, 2,2'-bipyridine, ethylenediaminetetraacetic acid, ethylenediamine, One or more of glycine. 4. The preparation method according to claim 1, wherein the copper salt is one or more of copper nitrate, copper sulfate and copper chloride. 5. preparation method according to claim 1 is characterized in that, the acidic solution used for etching in the described 3rd step is one or more in sulfuric acid, hydrochloric acid, nitric acid; The concentration of acidic solution is 0.1～ 10mol L ^-1 , the etching time is 1-48 hours, and the etching temperature is 50-120°C. 6. preparation method according to claim 1 is characterized in that, described first step solvent is one or more in water, ethanol, ethylene glycol; Solvent is water, ethanol, ethylene glycol in the second step One or more of diols. 7. The preparation method according to claim 1, characterized in that, the drying method in the second step is vacuum drying, air atmosphere drying, and inert atmosphere drying, the drying temperature is 50-150° C., and the drying time is 5-150° C. 48h. 8. The preparation method according to claim 1, wherein the drying method in the third step is vacuum drying, air atmosphere drying, inert atmosphere drying, freeze drying, and the drying temperature is -20 to 300°C. The time is 5-60 hours.

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