CN115172783A - Carbon-base-free loaded high-entropy alloy particle and preparation method and application thereof - Google Patents

Abstract

The invention discloses a carbon-base-free loaded high-entropy alloy particle and a preparation method and application thereof. The high-entropy alloy particles comprise platinum, iron, cobalt, nickel and copper in a molar ratio of 1: 0.5-2; the high-entropy alloy particles are single-phase solid solution alloys with face-centered cubic structures; the grain diameter of the high-entropy alloy particles is 4-20 nm. The high-entropy alloy particles have the advantages of low Pt loading capacity, high Pt utilization rate, high catalytic activity and high stability; the high-entropy alloy particles are applied as an oxygen reduction catalyst, and the initial mass activity reaches 0.57A mg _Pt ^‑1 And the activity retention rate can reach 84.2% after 5000 cycles of stability test.

Description

A kind of high-entropy alloy particles without carbon support and preparation method and application thereof

technical field

The invention relates to the technical field of fuel cell materials, and more particularly, to a carbon-free supported high-entropy alloy particle and a preparation method and application thereof.

Background technique

In order to cope with the continuous growth of energy demand and environmental pollution, accelerating the development of new energy has become a common choice for all countries in the world to maintain energy security, meet climate change, and achieve sustainable development. As a green energy conversion device, hydrogen fuel cell has the advantages of high energy conversion efficiency, low environmental pollution and high specific energy.

However, in the hydrogen-oxygen fuel cell electrode reaction, the kinetic process of the cathodic oxygen reduction reaction is very slow, and a high loading of precious metal platinum is required as a catalyst to ensure the power output efficiency; Under normal conditions, the oxidative dissolution, agglomeration, and poisoning of platinum catalysts accelerate their performance degradation, which makes it difficult to achieve large-scale commercialization of hydrogen fuel cells due to their high cost.

In view of the above problems, it is proposed to form binary and ternary alloys by alloying noble metal Pt with inexpensive transition metals (Co, Ni, Fe, Cu, etc.) to improve the activity and stability of Pt-based catalysts, while effectively reducing the amount of Pt. In order to further improve the utilization rate of Pt, the concept of high-entropy alloys is proposed by extending the design concept of binary alloys to multi-principal alloys. The prior art discloses a preparation method of a monodisperse platinum-based high-entropy alloy nanoparticle catalyst, and there are also reports that disclose a carbon-supported metal catalyst and its preparation method and application. Although the above-mentioned prior art improves the utilization rate of Pt and obtains high-entropy alloy catalysts with good dispersibility and good catalytic performance, all of them are carbon-based catalysts supported by carbon materials. However, the corrosion resistance of carbon materials is poor, and Pt nanoparticles gradually accumulate and grow during battery operation, resulting in lower and lower catalyst activity.

Aiming at the problem of carbon-based supported catalysts, the prior art discloses a method for preparing a platinum-based high-entropy alloy catalyst, which is synthesized by an ultrasonic-assisted chemical reduction method to achieve one-pot step-by-step synthesis of high-entropy alloy core nanoparticles and Pt shells synthesis. However, this method requires the use of surfactants and the reaction temperature is low, resulting in a low degree of alloying of the obtained material, and the particle size control of the high-entropy alloy catalyst cannot be achieved, resulting in poor catalytic performance of the platinum-based high-entropy alloy catalyst.

Therefore, it is necessary to develop a carbon-free supported HEA particle with better catalytic performance.

SUMMARY OF THE INVENTION

The present invention provides a high-entropy alloy particle without carbon-based support in order to overcome the defect of poor catalytic performance described in the prior art.

Another object of the present invention is to provide a method for preparing the above-mentioned carbon-free supported high-entropy alloy particles.

Another object of the present invention is to provide the application of the above-mentioned carbon-free supported high-entropy alloy particles.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A high-entropy alloy particle without carbon-based support, comprising platinum, iron, cobalt, nickel, copper;

The high-entropy alloy particles are single-phase solid solution alloys with a face-centered cubic structure;

The particle size of the high-entropy alloy particles is 4-20 nm.

The high-entropy alloy particles of the present invention do not have a carbon-based material as a carrier, and the five metal elements of platinum, iron, cobalt, nickel and copper are uniformly dispersed in a proportion close to an equimolar ratio, and have a high single-phase solid solution structure, and there is no individual element. Aggregation or segregation.

The average particle size of the high-entropy alloy particles is 8.8-11.2 nm. As a nano-sized alloy material, the high-entropy alloy particles have a very high utilization rate of platinum atoms, and can expose more highly active edge reaction sites, thereby improving the catalyst. active.

Preferably, the particle size of the high-entropy alloy particles is 4-13 nm.

Preferably, the molar ratio of platinum, iron, cobalt, nickel and copper is 1:1:1:1:1.

Preferably, the D90 particle size of the high-entropy alloy particles is 12.9 nm.

The present invention also protects the preparation method of the above-mentioned high-entropy alloy particles, comprising the following steps:

S1. The metal salt precursor solution of platinum, iron, cobalt, nickel and copper is introduced into the ordered pores of the molecular sieve by the two-solvent method, and after stirring and drying, the metal salt-molecular sieve precursor is obtained;

S2. obtain platinum-iron-cobalt-nickel-copper-molecular sieve by reducing the metal salt-molecular sieve precursor;

The reducing atmosphere is an argon-hydrogen mixture, the reduction temperature is 400-1000°C, and the temperature-programmed rate is 0.5-5°C/min;

S3. The molecular sieve template is removed by etching with a hydrofluoric acid solution to obtain high-entropy alloy particles without carbon support.

The preparation method of the present invention controls the final size of the nanoparticles by controlling the temperature-programmed rate of high-temperature reduction and regulating the release rate of the metal salt combined with water and gas products. Small-sized nanoparticles can greatly improve the utilization of platinum atoms and expose more highly active edge reaction sites, thereby improving catalyst activity.

During the high temperature reduction process, as the temperature gradually increases, the metal salt will go through three stages, namely, the melting of the metal salt, the loss of bound water, and finally the thermal decomposition and the release of gaseous products. When the reaction temperature reaches the melting point of the metal salt, the metal salt begins to melt and exists in the molecular sieve channel in a liquid state, which can flow relatively freely in the molecular sieve channel. The faster the heating rate is, the faster the combined water and gas products escape from the molecular sieve channels at the same time. Part of the liquid metal salt is squeezed out of the molecular sieve channels, and the particle size is larger and uneven. The reduction temperature significantly affects the crystal structure of the alloy, and the higher the reduction temperature, the higher the alloying degree of the alloy.

In addition, using molecular sieve as a hard template, the metal salt precursor was introduced into the ordered pores of the molecular sieve by the two-solvent method, and the ordered pore structure of the molecular sieve was used to adjust the particle size of the high-entropy alloy particles and effectively limit the high-entropy alloy. agglomeration of particles.

Through hydrofluoric acid etching, on the one hand, the molecular sieve can be removed, and on the other hand, the transition metal iron, cobalt, nickel and copper on the surface of the alloy nanoparticles can be selectively dissolved, forming more steps, holes, Defective sites such as edges can further increase the surface density of low-coordination active sites and greatly improve the catalytic reaction efficiency.

In the present invention, the two-solvent method utilizes a two-solvent system of cyclohexane and water. Specifically, it can be as follows: uniformly dispersing a certain mass of molecular sieve template in the non-polar solvent cyclohexane, taking the pore volume of a given mass of molecular sieve as the benchmark, and then slowly adding an equal volume of the metal salt precursor solution dropwise. Since cyclohexane is immiscible with water and cannot dissolve metal salts, the high interfacial tension between cyclohexane and the aqueous solution is used to drive, combined with ultrasonic dispersion, to achieve full and uniform impregnation of the molecular sieve pores in the aqueous solution of metal salt precursors.

Preferably, the inlet rate of the argon-hydrogen mixture is 50 mL/min.

Preferably, the volume ratio of hydrogen to argon in the reducing atmosphere is 5:95.

Preferably, the pore size of the molecular sieve is 6-10 nm, and the pore volume is 0.5-1.5 cm ³ /g.

Preferably, the metal salt precursor solution of platinum, iron, cobalt, nickel and copper is an aqueous solution of chloroplatinic acid, iron nitrate, cobalt nitrate, nickel nitrate and copper nitrate.

Preferably, the concentration of the metal salt precursor solution is 1˜30 wt.%. More preferably, the concentration of the metal salt precursor solution is 5-20 wt.%. Further preferably, the concentration of the metal salt precursor solution is 10-15 wt.%.

Preferably, the mass-volume ratio of the molecular sieve to the metal salt precursor solution is 0.5-1 g:0.5-1 ml.

More preferably, the mass-to-volume ratio of the molecular sieve to the metal salt precursor solution is 1 g:1 ml.

Preferably, the drying is carried out in a blast drying oven, the drying temperature is 60°C to 100°C, and the drying time is 12 to 24 hours.

Preferably, the reduction time is 0.5-10 hours.

Preferably, the reduction temperature is 600-1000°C; the temperature-programmed rate is 1-2°C/min.

More preferably, the reduction temperature is 900°C, and the temperature-programmed rate is 1°C/min.

Preferably, the concentration of the hydrofluoric acid solution is 4-40 wt.%, and the etching treatment time is 8-36 h.

More preferably, the etching treatment time is 10-24 h; further preferably, the etching treatment time is 12-20 h.

The present invention also protects the application of the above-mentioned high-entropy alloy particles as a redox catalyst in an oxygen reduction electrocatalytic reaction in an acidic system.

Specifically, the high-entropy alloy particles can be used as redox catalysts to catalyze oxygen reduction reactions at the cathode of fuel cells.

Compared with the prior art, the beneficial effects of the present invention are:

The present invention develops a high-entropy alloy particle without carbon-based support, which has the advantages of low Pt loading, high Pt utilization, high catalytic activity and high stability. The high-entropy alloy particles are used as oxygen reduction catalysts, and the initial mass activity reaches 0.57Amg _Pt ^-1 , which is about 4 times that of commercial Pt/C, and the activity retention rate can reach 84.2% after 5000 cycles in the stability test.

By controlling the high temperature reduction heating rate and the release rate of the metal salt combined with water and gas products, the invention can precisely control the final size of the nanoparticles. Small-sized nanoparticles can greatly improve the utilization rate of platinum atoms and expose more Highly active edge reaction sites; while removing molecular sieves by hydrofluoric acid etching, it can selectively dissolve transition metals iron, cobalt, nickel and copper on the surface of alloy nanoparticles, forming more steps and holes on the surface of nanoparticles , edge and other defect sites, further increase the surface density of low-coordination active sites, thereby improving the catalytic activity of high-entropy alloy particles.

Description of drawings

Fig. 1 is the preparation flow chart of the high-entropy alloy nanoparticle of the present invention;

Fig. 2 is the transmission electron microscope picture of the platinum-iron-cobalt-nickel-copper-molecular sieve obtained in step S2 in embodiment 1;

Fig. 3 is the transmission electron microscope picture of the high entropy alloy particle obtained in Example 1;

4 is an EDS-Mapping diagram of the high-entropy alloy particles prepared in Example 1;

Fig. 5 is the oxygen reduction polarization curve diagram of the high-entropy alloy particles prepared in Example 1 as a catalyst and a commercial platinum-carbon catalyst Pt/C;

6 is a polarization curve diagram of the high-entropy alloy particles obtained in Example 1 as a catalyst before and after a 5000-cycle cycle stability test;

7 is a schematic diagram of the mass specific activity and area specific activity of the high-entropy alloy particles prepared in Example 1 as a catalyst before and after 5000 cycle stability tests;

8 is the X-ray diffraction pattern of the high-entropy alloy particles of Example 1, Example 2, Example 3 and Comparative Example 2;

9 is a graph showing the oxygen reduction polarization curves of the high-entropy alloy particles of Example 1, Example 2, Example 3, and Comparative Example 2 and commercial pt/C;

10 is a graph showing the oxygen reduction polarization curves of the high-entropy alloy particles of Example 1, Example 4, and Comparative Example 1.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

The raw materials in the examples and comparative examples can be obtained commercially, wherein:

Molecular sieve-1, purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd., SBA15 molecular sieve, with a pore size of 6-10 nm and a pore volume of 1 cm ³ /g;

Molecular sieve-2, purchased from Aladdin Reagent Co., Ltd., KIT-6 molecular sieve, with an average pore size of 9.2 nm and a pore volume of 0.5-1.5 cm ³ /g;

Chloroplatinic acid hexahydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate and copper nitrate trihydrate were purchased from Aladdin Reagent Co., Ltd.

Commercial Pt/C, purchased from John Matthey Company.

Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

Example 1

The present embodiment provides a high-entropy alloy particle, and the preparation method includes the following steps:

S1. Add 1 g of SBA15 molecular sieve (molecular sieve-1, with a pore size of 6 to 10 nm and a pore volume of 1 cm ³ /g) and 30 ml of cyclohexane into a beaker, which is then stirred and sonicated to form a uniform suspension; Under the premise of 1 ml of metal salt precursor solution (containing 9.5 mg of chloroplatinic acid hexahydrate (H ₂ PtCl ₆ ·6H ₂ O), 5.6 mg of copper nitrate trihydrate (Cu(NO ₃ ) ₂ ·3H ₂ O), 9.3 mg of mg ferric nitrate nonahydrate (Fe(NO ₃ ) ₂ ·9H ₂ O), 6.7 mg cobalt nitrate hexahydrate (Co(NO ₃ ) ₂ ·6H ₂ O) and 6.7 mg nickel nitrate hexahydrate (Ni(NO ₃ ) ₂ 6H ₂ O) aqueous solution) was added dropwise to the beaker, and then ultrasonicated for half an hour to make the components uniformly dispersed, and then continued to stir until the solvent was completely volatilized to obtain a metal salt-molecular sieve precursor;

S2. evenly spread the metal salt-molecular sieve precursor into the corundum ark, put it into a tube furnace for high-temperature thermal reduction, and pass 30min of argon-hydrogen mixture (Ar:H ₎ before heating for heating. The volume ratio is 95: 5) To remove the air in the quartz tube, keep the air intake rate at 50mL/min; then heat to 900°C at a heating rate of 1°C/min for 1 hour, and naturally cool to room temperature to obtain platinum-iron-cobalt-nickel-copper-molecular sieve;

S3. Slowly add the above platinum-iron-cobalt-nickel-copper-molecular sieve into the centrifuge tube, add 30 ml of 4wt.% hydrofluoric acid solution, let stand for 24h to remove the molecular sieve template, then centrifuge and wash with deionized water, and place the sample in a blast drying oven After drying at 60 °C for 24 h, the obtained samples were ground evenly to obtain high-entropy alloy particles without carbon support.

The platinum-iron-cobalt-nickel-copper-molecular sieve obtained in step S2 is subjected to transmission electron microscopy detection, and the specific method is as follows: use the Tecnai G2 (F30) transmission electron microscope of the Netherlands FEI company with an energy dispersive spectrometer (Energy Dispersive Spectrometer, EDS). The morphology, crystal structure and elemental composition were analyzed. The samples with different thickness and surface roughness have different effects on the scattering of high-energy electron beams. The electromagnetic lens is used to collect the related signals of scattered electrons and present them on the fluorescent screen, so that the microscopic morphology of the samples can be observed. The TEM image is shown in Figure 2. It can be seen that the ordered pores of the molecular sieve effectively limit the agglomeration of the high-entropy alloy, and the high-entropy alloy is uniformly dispersed.

The high-entropy alloy particles obtained in step S3 are detected by transmission electron microscopy, and the transmission electron microscopy image is shown in FIG. 3 . It can be seen that the particle size of the high-entropy alloy is uniform, the particle size distribution of the nanoparticles is 4-15 nm, the D90 particle size is 12.9 nm, and the average particle size is 9.2 nm.

X-ray energy spectrum analysis is performed on the high-entropy alloy particles obtained in step S3, and the EDS-Mapping diagram is shown in FIG. 4 . It can be seen that the distribution of each metal element in the high-entropy alloy particles prepared in this example is highly uniform, and a large amount of agglomeration or segregation of metal elements is not found, and the molar ratio of platinum, iron, cobalt, nickel, and copper is about 1:1: 1:1:1. The X-ray diffraction pattern is shown in Figure 8, and it can be seen that the high-entropy alloy particles are single-phase solid solution alloys with a face-centered cubic structure.

Example 2

The present embodiment provides a high-entropy alloy particle, and the difference between the preparation method and the embodiment 1 is:

In step S2, in the reduction treatment, the air intake rate was 50 mL/min; then, the temperature was heated to 1000° C. at a heating rate of 1° C./min for 2 h.

The particle size distribution of the prepared high-entropy alloy particles is 4-13 nm, and the average particle size is 9.5 nm.

Example 3

The present embodiment provides a high-entropy alloy particle, and the difference between the preparation method and the embodiment 1 is:

In step S2, in the reduction treatment, the air intake rate was 50 mL/min; then, the temperature was heated to 800° C. at a heating rate of 1° C./min for 3 h.

The particle size distribution of the prepared high-entropy alloy particles is 4-13 nm, and the average particle size is 9.1 nm.

Example 4

The present embodiment provides a high-entropy alloy particle, and the difference between the preparation method and the embodiment 1 is:

In step S2, in the reduction treatment, the air intake rate is 50 mL/min; then, the temperature is heated to 900° C. at a heating rate of 0.5° C./min for 1 h.

The particle size distribution of the prepared high-entropy alloy particles is 4-13 nm, and the average particle size is 8.8 nm.

Example 5

The present embodiment provides a high-entropy alloy particle, and the difference between the preparation method and the embodiment 1 is:

In step S2, in the reduction treatment, the air inlet rate is 50 mL/min; then, the temperature is heated to 900° C. at a heating rate of 5° C./min for 1 h.

The particle size distribution of the prepared high-entropy alloy particles is 4-20 nm, and the average particle size is 11.8 nm.

Example 6

The present embodiment provides a high-entropy alloy particle, and the difference between the preparation method and the embodiment 1 is:

The molecular sieve used is molecular sieve-2 with a pore size of 9.2 nm and a pore volume of 0.5-1.5 cm ³ /g.

The particle size distribution of the prepared high-entropy alloy particles is 4-13 nm, and the average particle size is 11.2 nm.

Comparative Example 1

This comparative example provides a kind of high-entropy alloy particles, and the difference between the preparation method and Example 1 is:

In step S2, in the reduction treatment, the air intake rate was 50 mL/min; then, the temperature was heated to 900° C. at a heating rate of 10° C./min for 1 h.

The particle size distribution of the prepared high-entropy alloy particles is 12-54 nm, and the average particle size is 45.4 nm.

Comparative Example 2

This comparative example provides a kind of high-entropy alloy particles, and the difference between the preparation method and Example 1 is:

In step S2, in the reduction treatment, the air inlet rate is 50 mL/min; then, the temperature is heated to 400° C. at a heating rate of 1° C./min for 1 h.

The particle size distribution of the prepared high-entropy alloy particles is 4-13 nm, and the average particle size is 9.6 nm. According to the X-ray diffraction pattern of Comparative Example 2 in FIG. 8 , it can be seen that when the reduction temperature is too low, the alloying degree of the material is too low.

Catalytic performance test

Catalytic performance tests were carried out on the high-entropy alloy particles prepared in the above examples and comparative examples. The high-entropy alloy particles were used as the cathode material, the platinum sheet was used as the anode, the saturated calomel electrode was used as the reference electrode, and the 0.1M HClO ₄ aqueous solution was used. The specific method is as follows:

Oxygen reduction polarization curve analysis: Linear Scanning Voltammetry (LSV) was performed in _O2 -saturated 0.1M HClO4 aqueous solution with a potential scan range of 1.1 to 0.2V (vs. RHE) and a scan speed of 20mV/ s, set the electrode rotation speed to 1600 rpm.

Cyclic stability test: at room temperature, in O2-saturated 0.1M HClO4 aqueous solution, in the potential range of 0.6 to 1.0V (vs. RHE) at a scan rate of 50mV/s (Cyclic Voltammetry, CV) Test: Detect the polarization curve and mass specific activity and area specific activity before and after 5000 cycles.

Figure 5 is the oxygen reduction polarization curve diagram of the high-entropy alloy particles prepared in Example 1 as a catalyst and a commercial platinum-carbon catalyst Pt/C. It can be seen that the prepared high-entropy alloy particles as a catalyst have more excellent oxygen reduction The catalytic performance, with a half-wave potential of 0.892 V, is 42 mV higher than that of the commercial Pt/C catalyst.

Figure 6 shows the polarization curves of the high-entropy alloy particles prepared in Example 1 as a catalyst before and after 5000 cycles of cyclic stability testing; Figure 7 shows the high-entropy alloy particles prepared in Example 1 as a catalyst after 5000 cycles of cycle stability Schematic diagram of mass specific activity and area specific activity before and after the test. It can be found that the high-entropy alloy particles are used as oxygen reduction catalysts, and the initial mass activity reaches 0.57A mg _Pt ^-1 , which is about 4 times that of commercial Pt/C. After 5000 cycles of the stability test, the half-slope potential of the high-entropy alloy particles in Example 1 decreased by 11 mV, and the mass specific activity and area specific activity decreased by only 15.8% and 19.2%, respectively. Excellent stability.

According to the test results of the ORR polarization curves in FIGS. 9 and 10 , it can be seen that the examples of the present application have better ORR catalytic performance compared with Comparative Examples 1-2 and commercial Pt/C.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (10)

1. The carbon-free-based loaded high-entropy alloy particles are characterized by comprising platinum, iron, cobalt, nickel and copper in a molar ratio of 1: 0.5-2;

the high-entropy alloy particles are single-phase solid solution alloys with face-centered cubic structures;

the grain diameter of the high-entropy alloy particles is 4-20 nm.

2. A high entropy alloy particle according to claim 1, wherein the molar ratio of platinum, iron, cobalt, nickel and copper is 1: 1.

3. A high entropy alloy particle in accordance with claim 1, wherein the average particle diameter of the high entropy alloy particle is 8.8-11.2 nm.

4. A method for producing high-entropy alloy particles described in any one of claims 1 to 3, characterized by comprising the steps of:

s1, introducing a metal salt precursor solution of platinum, iron, cobalt, nickel and copper into ordered pore channels of a molecular sieve by a two-solvent method, and stirring and drying to obtain a metal salt-molecular sieve precursor;

s2, reducing the metal salt-molecular sieve precursor to obtain a platinum-iron-cobalt-nickel-copper-molecular sieve;

the reducing atmosphere is argon-hydrogen mixed gas, and the reducing temperature is 400-1000 ℃; the temperature programming rate is 0.5-5 ℃/min;

and S3, removing the molecular sieve template by etching with a hydrofluoric acid solution to obtain the carbon-base-free loaded high-entropy alloy particles.

5. The method according to claim 4, wherein the volume ratio of hydrogen to argon in the reducing atmosphere is 5:95.

6. the method according to claim 4, wherein the molecular sieve has a pore diameter of 6 to 10nm and a pore volume of 0.5 to 1.5cm ³ /g。

7. The preparation method according to claim 4, wherein the metal salt precursor solution of platinum, iron, cobalt, nickel, copper is an aqueous solution of chloroplatinic acid, iron nitrate, cobalt nitrate, nickel nitrate, and copper nitrate; preferably, the concentration of the metal salt precursor solution is 1 to 30wt.%.

8. The preparation method according to claim 4, wherein the mass-to-volume ratio of the molecular sieve to the metal salt precursor solution is 0.5-1 g: 0.5-1 ml.

9. The method according to claim 4, wherein the hydrofluoric acid solution has a concentration of 4wt.% and the etching time is 8-36 h.

10. Use of the high-entropy alloy particles of any one of claims 1 to 3 as a redox catalyst in an oxygen reduction electrocatalytic reaction in an acidic system.

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