CN115188978A

CN115188978A - Preparation method and application of supported polycrystalline surface defect high-entropy alloy catalyst

Info

Publication number: CN115188978A
Application number: CN202210937424.5A
Authority: CN
Inventors: 姚涛; 沈心怡; 曹林林; 张伟
Original assignee: University of Science and Technology of China USTC
Current assignee: Zhongke Enthalpy Anhui New Energy Technology Co ltd
Priority date: 2022-08-05
Filing date: 2022-08-05
Publication date: 2022-10-14
Anticipated expiration: 2042-08-05
Also published as: CN115188978B

Abstract

The invention relates to the field of alloy catalysts, and discloses a preparation method and application of a high-entropy alloy catalyst with supported polycrystalline surface defects, wherein the method comprises the following steps: s1, adding acetylacetone platinum into an oleylamine mixed solution of acetylacetone iron, acetylacetone cobalt and acetylacetone copper, adding a reducing agent borane tert-butylamine complex for reflux reaction for a period of time, cooling, washing and centrifuging a product, and performing ultrasonic stirring together with a carbon black n-hexane dispersion liquid to prepare a coralliform PtFeCoCu alloy loaded on carbon black; s2, carrying out ultrasonic cleaning, centrifuging and drying on the obtained PtFeCoCu alloy, and then annealing under hydrogen-argon mixed protective gas to prepare the supported catalyst with a specific structure. The coralline platinum-iron-cobalt-copper nano alloy catalyst with uniform dispersion and appearance is prepared by the invention, and the high-entropy alloy nano particles with special crystal face structures are obtained by further annealing and curing, and the obtained catalyst shows excellent oxygen reduction activity in an acid environment.

Description

Preparation method and application of supported high-entropy alloy catalyst with polycrystalline surface defects

Technical Field

The invention relates to the technical field of alloy catalyst synthesis, in particular to a preparation method and application of a supported alloy nanoparticle catalyst.

Background

Hydrogen fuel cells can convert hydrogen gas as fuel to obtain high energy density electric energy, but there are many problems in practical applications, such as slow kinetics rate of Oxygen Reduction Reaction (ORR) performed at the cathode, and therefore there is a need for developing a catalyst material with low cost, high energy conversion efficiency, and long lifetime.

Currently, the cathode oxygen reduction electrocatalyst of the existing commercial proton exchange membrane fuel cell is mainly a platinum-carbon (Pt/C) catalyst, which mainly uses noble metal Pt, and the price is high, and the activity and the stability of long-term operation still need to be further improved. High entropy alloy HEA, also known as multi-principal element alloy (MPEA), has attracted much attention due to its unique and attractive properties, showing great potential for application in many fields, and has become one of the hottest materials. HEA largely meets the requirements for being a proactive electrocatalyst due to the tunability of its constituent electronic structures and its significant stability in corrosive media. In the field of electrocatalytic oxygen reduction, pt has outstanding performance and occupies an important position, and the design of using the Pt-based high-entropy alloy as an electrocatalyst is hopeful to further solve the problems of low specific activity, poor stability and the like while reducing the use amount of noble metals.

Disclosure of Invention

In order to solve the defects in the background technology, the invention aims to provide a preparation method and application of a PtFeCoCu high-entropy alloy nanoparticle with a polycrystalline surface defect.

The purpose of the invention can be realized by the following technical scheme:

the invention provides a preparation method of a supported polycrystalline surface defect high-entropy alloy catalyst, which comprises the following steps:

s1, adding acetylacetone platinum into an oleylamine mixed solution of acetylacetone iron, acetylacetone cobalt and acetylacetone copper, adding a reducing agent borane tert-butylamine complex, placing the mixture into a circulating reflux heating environment protected by argon gas for stirring reaction for a period of time, naturally cooling a product to room temperature, performing ultrasonic treatment on the washed colloid under ethanol and n-hexane, performing centrifugal washing until no surfactant exists in the solution, performing ultrasonic treatment on the product obtained by centrifugation and an n-hexane dispersion liquid of carbon black together, and performing magnetic stirring and loading for 4-8 hours to prepare PtFeCoCu coral dendritic nanocrystals loaded on the carbon black;

s2, adding the obtained carbon black dispersion liquid of the PtFeCoCu coral dendritic nano-crystal into an ethanol solution for ultrasonic cleaning, centrifuging to obtain a product, performing vacuum drying, and annealing at different temperatures under hydrogen-argon mixed protective gas to prepare the supported catalyst with a specific morphology structure.

Further preferably, the molar ratio of platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate and copper acetylacetonate in step S1 is from 1.5 to 2.5.

Further preferably, in the initial stage of the step S1, the temperature is firstly increased to 120 ℃, the temperature is maintained for 30min, argon is introduced, then the temperature is increased to 250-350 ℃ at the temperature increasing rate of 5 ℃/min, and the reaction time is continued for 1-3h.

Further preferably, the loading rate of the centrifuged product on the carbon black in step S1 is 20%.

Further preferably, during the annealing in the step S2, the temperature is heated to 480-520 ℃ at a heating rate of 5 ℃/min, and then the temperature is kept for 3-5h, wherein the annealing is performed by adopting a hydrogen-argon mixed protective gas in which the volume ratio of hydrogen to argon is 1.

Use of a supported polycrystalline surface defect high-entropy alloy catalyst prepared according to the method of any one of claims 1 to 5 in an acid oxygen reduction reaction, wherein the polycrystalline surface defect PtFeCoCu high-entropy alloy nanoparticles have high-efficiency acid oxygen reduction reaction activity.

The invention has the beneficial effects that:

the invention provides a preparation method of a high-entropy alloy with a polycrystalline surface defect PtFeCoCu with high ORR activity, which utilizes a multi-element dendritic alloy nano cluster as a precursor, utilizes thermal annealing in-situ reconstruction to obtain small-size, short-range ordered and multi-domain polycrystalline PtFeCoCu high-entropy alloy nano particles, and under the combined action of atomic rearrangement, multi-element interaction and crystal surface defects, the Pt-based high-entropy alloy has a surface interface structure with special high activity, keeps smaller size and has no obvious grain size increase or phase separation.

The polycrystalline surface defect PtFeCoCu high-entropy alloy catalyst prepared by the method has high-efficiency acid oxygen reduction reaction activity, the size effect obviously improves the activity of the catalyst, and the polycrystalline surface defect PtFeCoCu high-entropy alloy not only improves the utilization rate of platinum atoms, but also reduces the cost of the catalyst. Meanwhile, the multi-element high-entropy alloy catalyst has higher activity and stability, and is a substitute of the electrocatalytic oxygen reduction catalyst with the most potential.

Drawings

The invention will be further described with reference to the accompanying drawings.

FIG. 1 is a process schematic diagram of the preparation method of the present invention;

FIG. 2 is a comparison of the X-ray diffraction patterns of examples 1, 2;

FIG. 3 is a transmission electron microscope photograph of PtFeCoCu after annealing in example 1

FIG. 4 is a transmission electron microscope photograph and a partially enlarged area photograph of a dark field image of PtFeCoCu after annealing in example 1; FIG. 5 is the EDS-Mapping elemental distribution of PtFeCoCu after annealing in example 1;

FIG. 6 is a comparison of the EXAFS maps of examples 1, 2;

FIG. 7 is a comparison of the performance of PtFeCoCu after annealing of example 1 after 10 k-turn accelerated cycle durability testing with commercial Pt/C;

FIG. 8 is a comparison of fuel cell performance tests of PtFeCoCu and commercial Pt/C after annealing in example 1;

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

0.5mmol of ferric acetylacetonate, 0.5mmol of cobalt acetylacetonate, 0.5mmol of copper acetylacetonate and 1mmol of platinum acetylacetonate are dispersed in 30ml of oleylamine, and then the precursor and the oleylamine are mixed and treated by ultrasonic wave for 20min, and 1mmol of borane-tert-butylamine complex TBAB is added for dissolution and dispersion. Next, the precursor solution was poured into a round flask and vigorously stirred and evacuated, and the solution was heated to 120 ℃ in reflux condensation mode and incubated for half an hour. Then argon is introduced, the temperature is raised to 300 ℃ at a heating rate of five degrees per minute under the protective atmosphere, and the temperature is kept for 1 hour.

And after the brown product colloidal solution is cooled to room temperature, performing centrifugal cleaning. Adding 30ml of n-hexane to disperse the product, adding 60 ml of ethanol to precipitate the product, shaking and carrying out ultrasonic treatment for five minutes to separate the product from oleylamine better, then carrying out centrifugal cleaning for 10 minutes at the speed of 8000 rpm, cleaning the product for three times according to the method, and removing the supernatant to obtain the product precipitate.

The product after cleaning is loaded on a carbon powder (XC-72) carrier in a proportion of 20wt%, the product and a certain amount of XC-72 carbon powder are jointly dispersed in an n-butylamine solvent for ultrasonic treatment for 30 minutes, and the loading is carried out in a magnetic stirring manner for 24 hours, so that ligand exchange and the deposition of nano particles on the carrier are fully carried out. Finally, the samples loaded on carbon black were washed with ethanol by centrifugation at 6000 rpm, three times and dried under vacuum overnight.

Example 2

0.5mmol of ferric acetylacetonate, 0.5mmol of cobalt acetylacetonate, 0.5mmol of copper acetylacetonate and 1mmol of platinum acetylacetonate are dispersed in 30ml of oleylamine, and then the precursor and the oleylamine are mixed and treated by ultrasonic wave for 20min, and 1mmol of borane-tert-butylamine complex TBAB is added for dissolution and dispersion. Next, the precursor solution was poured into a round flask and vigorously stirred and evacuated, and the solution was heated to 120 ℃ in reflux condensing mode for half an hour. Then argon is introduced, the temperature is raised to 300 ℃ at the temperature rise rate of five degrees per minute under the protective atmosphere, and the temperature is maintained for 1 hour.

And after the brown product colloidal solution is cooled to room temperature, performing centrifugal cleaning. Adding 30ml of n-hexane to disperse the product, adding 60 ml of ethanol to precipitate the product, shaking and performing ultrasonic treatment for five minutes to separate the product from oleylamine better, then performing centrifugal cleaning for 10 minutes at 8000 revolutions per minute, cleaning the product for three times according to the method, and removing supernatant to obtain product precipitate.

The product after cleaning is loaded on a carbon powder (XC-72) carrier in a proportion of 20wt%, the product and a certain amount of XC-72 carbon powder are dispersed in n-butylamine solvent together for ultrasonic treatment for 30 minutes, and the loading is carried out for 24 hours in a magnetic stirring manner, so that ligand exchange and the deposition of nano particles on the carrier are fully carried out. Finally, the samples loaded on carbon black were washed with ethanol by centrifugation at 6000 rpm, three times and dried under vacuum overnight. Placing the dried sample in 5% ₂ Per95% by volume, heated to 500 ℃ at a temperature-raising rate of 5 ℃ per minute, held for 4 hours, and then furnace-cooled.

Structure detection

From the XRD results of fig. 2, it can be seen that the annealed PtFeCoCu alloy catalyst supported on a carbon black substrate still maintains the fcc structure of Pt, and the shift of the diffraction peak to a high angle indicates that a transition metal of smaller atomic radius is incorporated into the crystal lattice, and in the sample of example 3, no diffraction peak of any single oxidized species occurs, indicating that the transition metal atom is incorporated into the crystal lattice of Pt, and no separate simple substance or oxide is formed. The width of the diffraction peak of PtFeCoCu after annealing becomes narrow, and the increase in the grain size after annealing is presumed. Further, as shown in fig. 3-4 of dark field TEM (fig. 3-4), the morphology of the PtFeCoCu alloy nanocrystals is largely changed before (a) and after (b) annealing, and the PtFeCoCu alloy nanocrystals are matured and reconstructed into nanoparticles with larger diameters from coral dendrite nanocrystals with small diameters. The element distribution image (fig. 5) analysis of the sample of example 3 shows that the distribution of the individual elements in the annealed PtFeCoCu sample is relatively uniform, and no element segregation or core-shell structure is formed. The HAADF-STEM image (FIG. 4) of the sample of example 3 shows that the surface of the sample has abundant crystal plane defects and is characterized by polycrystalline multidomain, which indicates that annealing causes the sample to be agglomerated and reconstructed, and the multi-orientation coral-shaped structure is gathered towards the center to be changed into nanoparticles with special crystal plane structures.

To further confirm that the annealed PtFeCoCu of example 3 exists in the form of an alloy, we characterized the material using Fourier transform X-ray fine structure absorption Spectroscopy (FT-EXAFS, FIG. 6), and it can be seen that example 2 is characterized by a major M-O nonmetal coordination peak and a minor M peak ₁ -M ₂ Metal coordination peak composition (M = Pt \ Fe \ CoCu), indicating that M is bonded to O at the alloy surface and has a certain oxidation state, confirming the formation and coordination environment of the annealed PtFeCoCu alloy, while the results of example 3 show a subpeak M of the annealed PtFeCoCu after annealing ₁ -M ₂ The height of the metal coordination peak is increased, the alloying degree is greatly improved, and the oxidation state is reduced. Finally, the above analysis results correspond to the electron microscope and XRD results, and the successful synthesis of the PtFeCoCu alloy catalyst supported on the carbon black substrate in example 3 is explained.

Performance detection

To evaluate the ORR activity under acidic conditions and the performance of the application of the PtFeCoCu alloy catalysts in examples 1, 2 to a proton exchange membrane fuel cell, we utilized commercial PtC (20%) catalyst as a performance control, with the following specific test procedures and results:

(1) 2mg of the PtFeCoCu alloy catalyst and the commercial PtC catalyst of examples 1 and 2 were respectively selected, 700. Mu.l of isopropanol and 180. Mu.l of ultrapure water were added, 20. Mu.l of perfluorosulfonic acid (5 wt%) was added as a binder, and the mixture was uniformly mixed and subjected to ultrasonic treatment for 1 hourA uniformly mixed catalyst ink was obtained. 20ml of catalyst ink is accurately transferred by a liquid transfer gun and uniformly dropped on a liquid drop with the diameter of 5mm and the area of 0.196cm ² The rotary disk electrode is naturally dried and then tested.

(2) At 0.1M HClO ₄ In the solution, ag/AgCl was used as a reference electrode, a platinum wire electrode was used as a counter electrode, measurements were made in a three-electrode mode and all potentials were converted to reversible hydrogen electrode potentials (RHE). The ORR polarization curves were collected at 1600rpm at a scan rate of 10 mV/s. Then saturated with nitrogen gas at room temperature under 0.1M HClO ₄ Accelerated cycling durability tests were performed in solution by applying a cycling potential sweep between 0.6 and 1.1V (vs. rhe) at a sweep rate of 100mV/s for 10000 cycles. When the ORR polarization curve is tested after the end of the cycle, and the results of the test are shown in fig. 7, it is evident that the PtFeCoCu catalyst of example 2 has the best ORR activity, has a half-wave potential of 0.95mV, much higher than 0.84mV of the commercial PtC catalyst, and has durability superior to that of PtC.

(3) To further test the performance of the PtFeCoCu catalyst in the fuel cell, 50mg of the PtFeCoCu catalyst after annealing of example 2 and the commercial PtC catalyst were mixed with 0.7ml of a 5-percent nafion solution, 1.5ml of isopropanol and 1.2ml of deionized water, respectively, and subjected to sonication for 1h, using commercial PtC as a control, to form a uniformly dispersed catalyst slurry in a high speed homogenizer (12000 rpm) for 15 min. Then, the well-dispersed catalyst ink was sprayed onto a piece of carbon paper (Dongli TGP-H-060) as a cathode with a platinum loading of 0.05mg Pt cm ^-2 .20wt% of Pt/C as a supporting amount of 0.15mg Pt cm ^-2 As a gas diffusion layer, having an effective area of 5cm ² . Then keeping the temperature at 130 ℃ for 90s under the pressure of 1MPa, and hot-pressing the prepared anode and cathode gas diffusion electrodes on two sides of the Nafion membrane to form a membrane electrode. We mounted the membrane electrode assembly in a single cell test fixture and tested using an 850E fuel cell test station. Hydrogen as fuel, oxygen/air as oxidant, humidified at 80 ℃, H ₂ The flow rate of (2) is 50CC min ^-1 ，O ₂ The flow rate of (2) is 20CC min ^-1 . When the battery is activated and stabilized, the polarization curve is followedThe increase in current density is recorded. In the whole test process, the temperature of the battery is 80 ℃, and the effective area is 5cm ² (ii) a The Relative Humidity (RH) of hydrogen and oxygen is 100%; an/Ca is 1.5/2.5. Prior to performance testing, the individual cells were continuously activated to achieve a steady state. When the battery activation is stable, the rule that the polarization curve increases with the current density is recorded. For the accelerated cycle aging test (ADT), pure hydrogen and pure nitrogen were injected into the anode and cathode, respectively, according to the DOE criteria. The cell voltage was driven by an external potentiostat with a square scan period between 0.6V and 0.95V. Each voltage level is held for 3s. It can be seen (FIG. 8) that the PtFeCoCu sample after annealing of example 2 reached 1.5A cm at 0.66V ^–2 The current density and the peak power density reach 1.54W cm ^–2 Is obviously higher than 830mW cm at 0.51V of Pt/C ^–2 Current density of (1.16W cm, peak current density) ^–2 。

In the description herein, references to the description of "one embodiment," "an example," "a specific example," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The foregoing shows and describes the general principles, principal features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed.

Claims

1. A preparation method of a supported polycrystalline surface defect high-entropy alloy catalyst is characterized by comprising the following steps:

2. A method for preparing a high-entropy alloy catalyst of supported polycrystalline surface defects according to claim 1, wherein the molar ratio of platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate and copper acetylacetonate in step S1 is 1.5-2.5.

3. A preparation method of a supported high-entropy alloy catalyst with polycrystalline surface defects according to claim 1, wherein in step S1, the temperature is raised to 120 ℃ at the initial stage, the temperature is kept for 30min, argon is introduced, then the temperature is raised to 250-350 ℃ at the temperature raising rate of 5 ℃/min, and the reaction time is continued for 1-3h.

4. A method for preparing a high entropy alloy catalyst of supported polycrystalline face defects according to claim 1, wherein the loading rate of the centrifuged product on the carbon black in the step S1 is 20%.

5. The method for preparing the supported high-entropy alloy catalyst for the polycrystalline surface defects according to claim 1, wherein the annealing in the step S2 is performed by heating to 480-520 ℃ at a heating rate of 5 ℃/min and then preserving heat for 3-5h, the volume ratio of hydrogen to argon in hydrogen-argon mixed protective gas is 1.

6. Use of a supported high-entropy alloy catalyst of polycrystalline surface defects in an acid oxygen reduction reaction, wherein the supported high-entropy alloy catalyst of polycrystalline surface defects is prepared according to the method of any one of claims 1 to 5, and the polycrystalline surface defects PtFeCoCu high-entropy alloy nanoparticles have high-efficiency acid oxygen reduction reaction activity.