Preparation method and application of s,n co-doped small nano-size high-entropy intermetallic compound

Abstract

The application discloses a preparation method and application of S, N co-doped small nano-size high-entropy intermetallic compound, and 2,2'-bithiophene is used as a metal ligand and a sulfur source in the synthesis of the high-entropy intermetallic compound for the first time. The sulfur atoms in the substance can form a complex with metal ions, so that the metal precursors can be uniformly and firmly distributed on the surface of a commercial carbon carrier, thereby facilitating the formation of the high-entropy intermetallic compound in a subsequent annealing process. The S, N co-doped high-entropy alloy intermetallic compound catalyst synthesized by the application has excellent electrochemical performance in a fuel cell, and has a significant performance in stability. The mass activity of the S, N co-doped high-entropy alloy intermetallic compound PtCuNiCoFe / C-SN (PCNCF-SN) catalyst reaches 2.7 A*mg at 0.9 V (vs. RHE), which is 12.3 times that of commercial Pt / C. ‑1 Pt In terms of stability, the mass activity can still remain above 65% after 100000 cycles of accelerated durability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fuel cell catalysts, and particularly relates to a catalyst for a cathode of a proton exchange membrane fuel cell, and particularly relates to a preparation method of synthesizing a small nano-sized high-entropy intermetallic compound on a carbon carrier and application thereof in a fuel cell. BACKGROUND

[0002] Hydrogen energy is a green and efficient perfect energy, and a proton exchange membrane fuel cell is one of efficient means for utilizing hydrogen energy, unlike traditional internal combustion engine technology, a direct chemical energy conversion into electrical energy breaks through the limitation of Carnot cycle, thereby greatly improving the energy conversion efficiency, and due to the advantages of high efficiency, zero pollution of products, rich application scenarios and the like, the proton exchange membrane fuel cell is highly concerned in the field of energy research.

[0003] However, the oxygen reduction reaction of the cathode of the proton exchange membrane fuel cell still faces the problem of slow kinetics, and the current fuel cell catalyst is still mainly platinum, and due to the low reserves and high price of platinum and poor cycle stability, the large-scale commercial application of the fuel cell is greatly limited. Although a large number of catalysts have been reported, there are certain problems in one or more aspects such as synthesis difficulty, activity and stability, and it is difficult to balance simple synthesis and high performance. Therefore, it is of great significance to develop a simple synthesis, strong universality and low-cost synthesis method to synthesize a new type of catalyst with high activity and high stability.

[0004] The high-entropy intermetallic compound has excellent activity and stability due to the high-entropy effect and ordered structure, and particularly has outstanding stability. However, the synthesis conditions are relatively harsh, and a series of problems caused by the high-temperature annealing step are usually faced, such as the most serious catalyst particle aggregation affecting the performance. In order to solve this key problem, a carbon carrier or template with special confinement effect is usually constructed to inhibit the aggregation and growth of particles, but this step undoubtedly increases the synthesis difficulty and cost, and is not conducive to the large-scale production and application of the catalyst.

[0005] In summary, in order to solve these problems, the present application proposes a simple step, strong universality and low-cost synthesis method to efficiently synthesize a high-entropy intermetallic compound, and the synthesized catalyst has excellent activity and stability in oxygen reduction catalysis. SUMMARY

[0006] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification of the present application in order to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and provide a preparation method of S, N co-doped small nano-size high-entropy intermetallic compounds.

[0009] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of S, N co-doped small nano-size high-entropy intermetallic compounds, comprising,

[0010] The noble metal salt, the transition metal salt, the sulfur source and the nitrogen source are added to the organic solvent, stirred at room temperature, and the carbon carrier is added and stirred at room temperature to obtain a mixture, and the mixture is ultrasonically treated to form a uniform mixture A;

[0011] The mixture A is stirred at room temperature, the organic solvent is evaporated by heating, and a black viscous paste B is formed, which is transferred to a vacuum oven for drying to obtain an intermediate product;

[0012] The intermediate product is annealed at high temperature in a reducing atmosphere to obtain S, N co-doped small nano-size high-entropy intermetallic compounds;

[0013] The sulfur source includes 2,2'-bithiophene, and the organic solvent includes acetone.

[0014] The S, N co-doped small nano-size high-entropy intermetallic compounds include carbon carriers containing S and N co-doped heteroatom sites, metal monatomic sites, and high-entropy intermetallic compounds loaded on the carbon substrate;

[0015] The S, N co-doped small nano-size high-entropy intermetallic compounds include high-entropy intermetallic compound particles composed of five or more metal elements;

[0016] The particle size of the S, N co-doped small nano-size high-entropy intermetallic compound particles is 2-5 nm.

[0017] As a preferred scheme of the preparation method of the present application, wherein: the noble metal salt includes at least one of platinum salt, iridium salt and palladium salt;

[0018] The platinum salt is platinum acetylacetone, the iridium salt is iridium acetylacetone, and the palladium salt is palladium acetylacetone.

[0019] As a preferred scheme of the preparation method of the present application, wherein: the transition metal salt is at least three or more combinations of copper salt, nickel salt, cobalt salt, iron salt, manganese salt and chromium salt;

[0020] The copper salt is acetylacetone copper, the nickel salt is acetylacetone nickel, the cobalt salt is acetylacetone cobalt, the iron salt is acetylacetone iron, the manganese salt is acetylacetone manganese and the chromium salt is acetylacetone chromium.

[0021] As a preferred scheme of the preparation method, the nitrogen source is any one of melamine, pipemidic acid, aminoantipyrine, triaminopyrazole and pyridine.

[0022] As a preferred scheme of the preparation method, the carbon carrier is at least one of carbon black, carbon nanotube and ketjen black.

[0023] As a preferred scheme of the preparation method, the molar ratio of the noble metal salt to the transition metal salt is (6-8):5, the mass ratio of the noble metal salt to the carbon carrier is (3-4):10, and the mass ratio of the sulfur source, the nitrogen source and the carbon carrier is 1-2:1-2:1-12.

[0024] As a preferred scheme of the preparation method, the carbon carrier is stirred at room temperature to obtain a mixture, wherein the stirring time is 30-60 min; the mixture is ultrasonically treated to form a uniform mixture A, wherein the ultrasonic treatment time is 1-4 h; the organic solvent is evaporated at a temperature of 70 DEG C for 0.5-1 h; and B is transferred to a vacuum oven for drying, wherein the drying temperature is 60 DEG C and the drying time is 12-24 h.

[0025] As a preferred scheme of the preparation method, the high-temperature annealing atmosphere is 10% H2 / Ar, the annealing temperature is 800-1000 DEG C, the annealing time is 2-4 h, and the annealing temperature rising rate is 3-5 DEG C / min.

[0026] Another object of the present application is to provide an S,N co-doped small nanometer size high-entropy intermetallic compound.

[0027] Another object of the present application is to provide an application of the S,N co-doped small nanometer size high-entropy intermetallic compound in the cathode oxygen reduction reaction of a proton exchange membrane fuel cell.

[0028] The present application has the following advantages:

[0029] (1) The present application first applies 2,2'-bithiophene as a metal ligand and a sulfur source to the synthesis of high-entropy intermetallic compounds, and since the sulfur atoms in the substance form a complex with metal ions, the metal precursors can be uniformly and firmly distributed on the surface of the commercial carbon carrier, so as to facilitate the formation of high-entropy intermetallic compounds in the subsequent annealing process; at the same time, the anchoring effect of S elements can not only inhibit the increase of catalyst particles during the annealing process, but also directly use commercial carbon carriers without the need to prepare special carbon carriers or pretreat the carbon carriers, thereby greatly reducing the cost and simplifying the steps.

[0030] (2) The use of acetone solvent in the present application has the characteristics of low boiling point and easy recovery, which can further reduce the cost; in addition, the introduction of multiple transition metals and non-metallic elements in the high-entropy intermetallic compound catalyst greatly reduces the amount of noble metal platinum, further reducing the cost of the catalyst; the synthesis method synthesizes S,N co-doped high-entropy intermetallic compounds with small nanometer size in one step through a simple impregnation method and subsequent high-temperature annealing; from the material, not only the synthesis of high-entropy intermetallic compound catalyst particles is realized in one step, but also non-metallic elements N and S are co-doped on the carbon substrate and M-N, M-S single-atom sites are formed; from the synthesis method, it is simple, easy to operate, low in cost, high in repeatability, high in purity and crystallinity of the synthesized material.

[0031] (3) The synthesis method proposed in the present application has universality and expandability to multiple metal elements; in theory, platinum group metals (PGMs) such as Ir, Pd, Ru, and Rh, which have similar chemical properties to Pt, are easily mixed randomly at the same crystallographic site, while elements such as copper, nickel, cobalt, iron, chromium, and manganese in 4d transition metals are metal elements with significantly different atomic radii and electronegativity from platinum group metals. Therefore, after successfully synthesizing a high-entropy intermetallic compound containing platinum, copper, nickel, cobalt, and iron, it is deduced that a series of high-entropy intermetallic compounds composed of platinum group elements and elements in 4d transition metals can be prepared by the synthesis method of the present application, and this is verified by successfully synthesizing an eight-element super-high-entropy intermetallic compound after adding three elements of iridium, manganese, and chromium.

[0032] (4) The S,N co-doped high-entropy alloy intermetallic compound catalyst synthesized in the present application has excellent electrochemical performance in fuel cells, especially in stability; among them, the mass activity of the S,N co-doped high-entropy alloy intermetallic compound PtCuNiCoFe / C-SN (PCNCF-SN) catalyst at 0.9V (vs. RHE) reaches 2.7A / mg Pt, which is 12.3 times more than that of commercial Pt / C; in terms of stability, the mass activity can still maintain more than 65% after 100000 cycles of accelerated durability, which is greatly improved compared with the commercial Pt / C catalyst; in addition, the peak power density of the hydrogen-air fuel cell constructed by using the catalyst as the cathode reaches 0.66 W / cm 2 ; the retention rate of the peak power density after 20000 cycles of accelerated durability reaches more than 75%, which indicates the excellent stability of the catalyst in the membrane electrode; the peak power density of the low-S, N content co-doped high-entropy alloy intermetallic compound PtCuNiCoFe / C-Low-SN (PCNCF-LSN) catalyst in the membrane electrode reaches 0.93 W / cm 2 . BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative labor. Among them:

[0034] Figure 1 is a transmission electron microscope (TEM) image of the catalyst PCNCF-SN prepared in Example 1.

[0035] Figure 2 is a particle size size statistical distribution graph of the catalyst PCNCF-SN prepared in Example 1.

[0036] Figure 3 is an X-ray diffraction graph of the catalyst PCNCF-SN prepared in Example 1 and commercial Pt / C.

[0037] Figure 4 is an X-ray photoelectron spectroscopy (XPS) of nitrogen (a) and sulfur (b) elements in the catalyst PCNCF-SN prepared in Example 1.

[0038] Figure 5 is a polarization curve graph of the catalyst PCNCF-SN prepared in Example 1 and the commercial Pt / C catalyst in the catalytic oxygen reduction reaction in 0.1 mol per liter of perchloric acid solution.

[0039] Figure 6 is a polarization curve graph of the catalyst PCNCF-SN prepared in Example 1 after accelerated durability test (ADT).

[0040] Figure 7 is a mass activity change column chart of the catalyst PCNCF-SN prepared in Example 1 at the initial, 40,000 cycles, 70,000 cycles and 100,000 cycles.

[0041] Figure 8 Polarization curves and power density plots of hydrogen-air fuel cell built with the material obtained in Example 1 as cathode and commercial Pt / C (20% TKK) as anode before and after accelerated durability test (AST).

[0042] Figure 9 Polarization curves and power density plots of hydrogen-air fuel cell built with the material obtained in Example 2 as cathode material and commercial Pt / C (20% TKK) as anode after short-term activation (4h) and long-term activation (14h).

[0043] Figure 10 X-ray diffraction patterns of the catalyst PtIrCuNiCoFeCrMn / C-SN (PICNCFCM-SN for short) prepared in Example 3 and Pt / C.

[0044] Figure 11 Elemental energy dispersive X-ray spectroscopy (EDX) of the catalyst PtIrCuNiCoFeCrMn / C-SN (PICNCFCM-SN for short) prepared in Example 3.

[0045] Figure 12 Transmission electron microscopy (TEM) of PtCuNiCoFe / C (PCNCF for short) prepared in Comparative Example 1.

[0046] Figure 13 X-ray diffraction patterns of PtCuNiCoFe / C (PCNCF for short) prepared in Comparative Example 1 and commercial Pt / C.

[0047] Figure 14 Polarization curves of PtCuNiCoFe / C (PCNCF for short) prepared in Comparative Example 1 and the catalyst PCNCF-SN obtained in Example 1 in 0.1 mole per liter of high-chlorate solution in catalyzing oxygen reduction reaction.

[0048] Figure 15 X-ray diffraction patterns of PCNCF-S obtained in Comparative Example 2, PCNCF-SN prepared in Example 1 and PCNCF obtained in Comparative Example 1.

[0049] Figure 16 Polarization curves of PCNCF-S obtained in Comparative Example 2 and PCNCF-SN prepared in Example 1 in 0.1 mole per liter of high-chlorate solution in catalyzing oxygen reduction reaction.

[0050] Figure 17X-ray diffraction patterns of PCNCF-piperazine, PCNCF-thiourea-piperazine, PCNCF-1,2 dimethylimidazole-piperazine prepared in Comparative Example 3, PCNCF-methanol prepared in Comparative Example 4, and PCNCF-SN prepared in Example 1.

[0051] Figure 18 Polarization curves of PCNCF-piperazine, PCNCF-thiourea-piperazine, PCNCF-1,2 dimethylimidazole-piperazine prepared in Comparative Example 3, PCNCF-methanol prepared in Comparative Example 4, and PCNCF-SN prepared in Example 1, when catalyzing oxygen reduction reaction in 0.1 mole per liter of high-chloric acid solution. DETAILED DESCRIPTION

[0052] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the embodiments of the present application.

[0053] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the concept of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0054] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is separate or alternative to other embodiments.

[0055] The specific information of raw materials used in the embodiments and comparative examples of the present application is as follows:

[0056] Metal precursor materials: platinum acetylacetonate (97%), iridium acetylacetonate (97%), copper acetylacetonate (97%), nickel acetylacetonate (95%), cobalt acetylacetonate (97%), iron acetylacetonate (98%), chromium acetylacetonate (98%), and manganese acetylacetonate (97%); wherein the iridium acetylacetonate (97%) is from Sigma-Aldrich manufacturer, and the rest of the reagents are from the McKin manufacturer.

[0057] Non-metallic sources: 2,2'-bithiophene (98%, Aldrich), piperazine (98%, Aldrich), thiourea (99%, McKin), 1,2 dimethylimidazole (99%, McKin).

[0058] Carbon material: Ketjen black (ECP-600JD, Kuraray).

[0059] Solvents: acetone (analytical grade 500 mL, Sinopharm Chemical Reagent Co., Ltd.), methanol (gradient grade M6600-4L, InoKai).

[0060] Materials used in electrochemical tests in the embodiments of the present application: deionized water (18.2 MΩ*cm@25℃), perchloric acid (super-pure 500 mL 74%-76%, Sinopharm Chemical Reagent Co., Ltd.), Nafion solution (D5205% 10 mL, Suzhou Sheng'Ernu Technology Co., Ltd.), anhydrous ethanol (analytical pure 500 mL, Sinopharm Chemical Reagent Co., Ltd.).

[0061] Example 1

[0062] The present embodiment provides a preparation method of an S, N co-doped small nano-sized high-entropy intermetallic compound catalyst PtCuNiCoFe / C-SN (referred to as PCNCF-SN), comprising the following steps:

[0063] (1) 9.5 mg of platinum acetylacetonate, 5.4 mg of copper acetylacetonate, 5.4 mg of nickel acetylacetonate, 5.3 mg of cobalt acetylacetonate, 7.2 mg of iron acetylacetonate, 20 mg of 2,2'-bithiophene, and 20 mg of pipemidic acid are added to a reaction container;

[0064] Then 20 ml of acetone is added to form a uniform orange yellow solution (containing a small amount of undissolved pipemidic acid); the solution is stirred at a speed of 500 r / min, and 50 mg of Ketjen black is gradually added during stirring; after the black suspension is formed, stirring is continued at a speed of 500 r / min for 30 min, and then the black suspension is ultrasonically treated for 1 h;

[0065] The black suspension is transferred to a beaker, and the temperature is increased to 70℃ while stirring, so as to evaporate most of the acetone to obtain a black slurry; the black slurry is transferred to a vacuum oven at 60℃ and dried for 12 h;

[0066] (2) The sample obtained in step (1) is transferred to a crucible, and heat treated at 800℃ at a speed of 3℃ / min in 10% H2-Ar (hydrogen volume ratio is 10%) for 4 h, and then naturally cooled to room temperature to obtain an S, N co-doped PtCuNiCoFe / C-SN (PCNCF-SN) high-entropy intermetallic compound nanocatalyst;

[0067] Figure 1 is a transmission electron microscope image of the PCNCF-SN catalyst material prepared in Example 1; Figure 2 is a particle size distribution frequency histogram of the PCNCF-SN catalyst. From Figure 1 and Figure 2 It can be seen that the PCNCF-SN catalyst particles prepared in Example 1 are uniformly dispersed on the carbon carrier, and the average particle size is 3.8 nm.

[0068] Figure 3 is the X-ray diffraction pattern of the PCNCF-SN catalyst material prepared in Example 1; from the figure, it can be seen that, similar to Pt / C, PCNCF-SN also forms a FCC single-phase structure dominated by (111) crystal faces, without segregation of other transition metal phases. In addition, each diffraction peak shifts to a higher angle, indicating that the doping of transition metals causes a certain lattice shrinkage, and the appearance of ordered diffraction peaks (asterisk) indicates the formation of high-entropy intermetallic compounds.

[0069] Table 1 is the mass fraction of each metal element of the PCNCF-SN catalyst material prepared in Example 1 measured by inductively coupled plasma atomic emission spectrometry;

[0070] Element class Pt Cu Ni Co Fe Mass fraction 5.5％ 1.9％ 1.5％ 1.6％ 1.1％

[0071] It can be seen that the total amount of metal is about 11% by mass fraction, and the proportion of platinum element is about half, and the other metal elements are similar to 1-2%.

[0072] Figure 4 is the X-ray photoelectron spectroscopy of sulfur (a), nitrogen (b) elements in the PCNCF-SN catalyst material prepared in Example 1; it can be observed that metal-nitrogen bonds (M-N), metal-sulfur bonds (M-S) and N, S heteroatomic sites are formed on the carbon substrate, which are beneficial to anchor the synthesized high-entropy intermetallic compound catalyst particles on the carbon carrier.

[0073] Take 20 mg of the PCNCF-SN catalyst prepared in Example 1, mix with 990 μL of anhydrous ethanol and 10 μL of Nafion solution, and ultrasonically treat the mixture for 1 h to obtain a uniformly mixed black ink.

[0074] Use a pipette to draw the catalyst ink and coat it on a glassy carbon (GC) electrode with a diameter of 5 mm, which serves as the working electrode, a platinum wire electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a 0.1 M perchloric acid solution as the electrolyte to form a three-electrode test system; under this system, the catalyst is tested, oxygen is continuously introduced, and cyclic voltammetry (CV) scanning is performed under the condition that the dissolved oxygen in the electrolyte is sufficient to activate the catalyst, the scanning range is-0.05V~0.95V, the scanning speed is 200mV s -1 , and the scanning number is 60; after activation, linear sweep voltammetry (LSV) test is performed, the scanning range is-0.05V~1.05V, the scanning speed is 10mV s -1 , and the polarization curve of the catalyst is obtained.

[0075] The specific steps of the accelerated durability test (ADT) of PCNCF-SN catalyst are as follows: 100000 cycles of CV scanning are performed, the scanning range is 0.4V-0.9V (relative to reversible hydrogen electrode), and the scanning speed is 200mV s -1 LSV tests are performed at 40000, 70000 and 100000 cycles respectively to obtain the polarization curves after accelerated durability.

[0076] Figure 5 The polarization curve diagram of the PCNCF-SN catalyst material prepared in Example 1 in a half-cell; it can be found that the half-wave potential of the material prepared by the method has a 60mV improvement compared with the commercial Pt / C catalyst, which represents a substantial improvement in the activity of the catalyst.

[0077] Figure 6 is the polarization curve diagram of the PCNCF-SN catalyst material prepared in Example 1 after accelerated durability test;

[0078] Figure 7 is the polarization curve diagram of the PCNCF-SN catalyst material prepared in Example 1 after accelerated durability test; Figure 6 The calculated catalyst mass activity decay histogram; the current density at 0.9V and 0.4V in the LSV curve is taken, the kinetic current density is calculated by the Koutecky-Levich equation, and the mass activity (MA) of the catalyst is obtained by normalizing the noble metal mass; from the above two diagrams, it can be seen that the mass activity only loses 34.2% after 100000 cycles of circulation, and the decay of the polarization curve is not obvious, which represents that the material prepared by the method has excellent stability.

[0079] Figure 8 is the polarization curve and power density diagram of the hydrogen-air fuel cell constructed by using the material obtained in Example 1 as the cathode and the commercial Pt / C (20% TKK) as the anode before and after accelerated durability test (AST); it can be seen from the diagram that the initial peak power density reaches 0.66W / cm 2 ; the peak power density retention rate is still more than 75% after 20000 cycles of accelerated durability circulation, which illustrates the excellent stability of the catalyst in the membrane electrode; it is worth mentioning that the current density of the polarization curve after 20000 cycles of circulation is higher than that of the polarization curve before circulation (i.e. the hollow triangular curve is above the green hollow circular curve), which illustrates that the activity of the catalyst after circulation is slightly improved; however, when the voltage drops below 0.6 volts, the corresponding current density drops faster, which illustrates that in the high current area, mass transfer resistance is the main reason for the decline in catalyst activity and performance after circulation.

[0080] Example 2

[0081] The embodiment provides a preparation method of a low-S, N content S, N co-doped small nano-size high-entropy intermetallic compound catalyst PtCuNiCoFe / C-Low-SN (PCNCF-LSN for short), which is a variation of the embodiment 1, and the difference is that the mass ratio of 2,2'-bithiophene and piperazine to the carbon carrier is adjusted to 1:10, and the other steps are the same as those of the embodiment 1.

[0082] Figure 9 Polarization curves and power density maps of a hydrogen-air fuel cell constructed by using the material obtained in the embodiment 2 as a cathode and a commercial Pt / C (20% TKK) as an anode after short-time activation (4h) and long-time activation (14h); it can be found that the performance of the catalyst with changed S, N content in the membrane electrode is better, and the peak power density reaches 0.75 W / cm 2 after 4h of activation, and the performance is further improved to 0.93 W / cm 2 It is found that regulating the content of nonmetallic elements can further improve the performance expression of the catalyst in the membrane electrode.

[0083] Embodiment 3

[0084] The embodiment provides a preparation method of an S, N co-doped small nano-size high-entropy intermetallic compound catalyst PtIrCuNiCoFeCrMn / C-SN (PICNCFCM-SN for short), which is a variation of the embodiment 1, and the difference is that the components of noble metals and transition metals are increased, and an ultra-high-entropy intermetallic compound composed of eight metal elements is prepared, and the specific steps include the following steps.

[0085] (1) 9.5 mg of platinum acetylacetonate, 11.2 mg of iridium acetylacetonate, 5.4 mg of copper acetylacetonate, 5.4 mg of nickel acetylacetonate, 5.3 mg of cobalt acetylacetonate, 7.2 mg of iron acetylacetonate, 54 mg of chromium acetylacetonate, 56 mg of manganese acetylacetonate, 20 mg of 2,2'-bithiophene and 20 mg of piperazine are added into a reaction container; then 20 ml of acetone is added to form a uniform orange yellow solution (containing a small amount of undissolved piperazine); the solution is stirred at a speed of 500 r / min, and 50 mg of ketjen black is gradually added during the stirring process; after the black suspension is formed, the stirring is continued at a speed of 500 r / min for 30 min, and then the black suspension is ultrasonically treated for 1 h; the black suspension is transferred to a beaker, and the temperature is increased to 70 DEG C while stirring, so that most of the acetone is evaporated to obtain a black slurry; the black slurry is transferred to a vacuum oven at 60 DEG C and dried for 12 h;

[0086] The sample obtained in (1) was transferred into a crucible, and heat-treated at 1000℃ for 4h at a rate of 3℃ / min in 10% H2-Ar, and after natural cooling to room temperature, an S, N co-doped PtIrCuNiCoFeCrMn / C-SN high-entropy intermetallic compound nanocatalyst was obtained;

[0087] Figure 10 is the X-ray diffraction pattern of the PtIrCuNiCoFeCrMn-SN catalyst material prepared in Example 2; ordered diffraction peaks can be observed in the figure, and there is no metal segregation impurity peak, indicating that a high-entropy intermetallic compound structure is formed.

[0088]

[0089] Figure 11 and the scanning electron microscope-X-ray energy dispersive spectrometer (SEM-EDX) spectrum and element quantitative data of the catalyst PICNCFCM-SN prepared in Example 2 of Table 2;

[0090] The element content obtained by scanning electron microscope-X-ray energy dispersive spectrometer (SEM-EDX) of the catalyst PICNCFCM-SN prepared in Example 2 of Table 2

[0091] From this data, it can be seen that the super high-entropy alloy is successfully synthesized, and the normalized mass fraction of each metal element is more than 5%, which meets the definition of high-entropy alloy.

[0092] In summary Figure 10 、 Figure 11 and Table 2, it is shown that a non-segregated super high-entropy alloy is synthesized by this method, which demonstrates the superiority of this method in the synthesis of high-entropy alloy catalysts.

[0093] Comparative Example 1

[0094] This comparative example aims to verify that the introduction of S, N organic compound raw materials (such as 2,2'-dithiophene and piperazine) in the preparation method of the present application is crucial to the successful preparation and performance of the final catalyst.

[0095] The catalyst PtCuNiCoFe / C (abbreviated as PCNCF) in this comparative example was prepared by the same steps as in Example 1, except that 2,2'-dithiophene and piperazine were not added, and other conditions were the same as in Example 1.

[0096] Figure 12 is the transmission electron microscope image of PCNCF prepared in Comparative Example 1; from the figure, it can be clearly seen that the particle size of the synthesized material is large and the aggregation phenomenon is obvious, which shows that the introduction of 2,2'-dithiophene and piperazine plays a crucial role in the success of synthesis.

[0097] Figure 13 is the X-ray diffraction pattern of PCNCF prepared in Comparative Example 1; from the figure, it can be seen that the position of the diffraction peak changes, indicating that no non-metallic element is introduced, the lattice compression is more obvious, and the diffraction peak is narrowed, which indicates that the particle size of the synthesized catalyst is larger, which is consistent with the results of Figure 10 .

[0098] Comparative Example 1 in the polarization curve test process of half cell with Example 1.

[0099] Figure 14 is the polarization curve comparison diagram of PCNCF prepared in Comparative Example 1 and PCNCF-SN catalyst prepared in Example 1 in the half cell; it can be seen from the figure that without adding 2,2'-bithiophene and piperazine, the catalytic performance of PCNCF is seriously reduced, far less than PCNCF-SN, which shows that the introduction of 2,2'-bithiophene and piperazine has a direct impact on the catalytic performance of the synthesized material. The above results show that the introduction of non-metallic elements (S, N) in the organic compound in the present application has a very important influence on the synthesis and catalytic performance of the material.

[0100] Comparative Example 2

[0101] This comparative example aims to verify the different effects of the introduction of S-containing organic compound raw material (2,2'-bithiophene) and nitrogen-containing raw material (piperazine) in the preparation method of the present application on the synthesis and performance of the catalyst.

[0102] The catalyst PtCuNiCoFe / C-S (abbreviated as PCNCF-S) in this comparative example is prepared by the same steps as in Example 1, except that piperazine is not added, and other conditions are the same as in Example 1.

[0103] Figure 15 is the comparison diagram of X-ray diffraction of the catalysts prepared in Comparative Example 2 and Comparative Example 1 and Example 1;

[0104] Comparative Example 2 in the polarization curve test process of half cell with Example 1.

[0105] Figure 16 is the polarization curve comparison diagram of PCNCF-S catalyst prepared in Comparative Example 3 and PCNCF-SN catalyst prepared in Example 1 in the half cell. From Figure 14 , it can be seen that compared with PCNCF without introducing S and N non-metallic sources, the introduction of S can enhance the anchoring effect of the carrier and greatly reduce the particle size of the particles;

[0106] From Figure 16As can be seen from the figure, the catalyst activity of PCNCF-S alone is far less than that of PCNCF-SN; as can be seen from the comparative example, the introduction of S element largely makes the particles keep small size, and the introduction of N element is very critical for high activity.

[0107] Comparative Example 3

[0108] The present comparative example aims to verify that 2,2'-bithiophene as a ligand and sulfur source plays a key role in the successful preparation of the catalyst and catalytic performance.

[0109] The three catalysts in the present comparative example are prepared by the same procedure as in Example 1, and are named as PCNCF-piperazine, PCNCF-thiourea-piperazine and PCNCF-1,2 dimethyl imidazole-piperazine, respectively, with the difference that: (1) 2,2'-bithiophene is not added; (2) thiourea is used to replace 2,2'-bithiophene; (3) 1,2 dimethyl imidazole is used to replace 2,2'-bithiophene, and other conditions are the same as in Example 1.

[0110] Figure 17 The indigo blue curve in the figure is the X-ray diffraction pattern of PCNCF-piperazine prepared in the comparative example. As can be seen from the figure, the peak shape of the diffraction peak is not symmetrical, which indicates that PCNCF-piperazine catalyst prepared without 2,2'-bithiophene has segregation. In addition, the absence of ordered characteristic peaks indicates that PCNCF-piperazine is not a high-entropy intermetallic compound. The above results show that the ligand effect of 2,2'-bithiophene is critical to the synthesis method.

[0111] Comparative Example 3 is tested in the same way as in Example 1.

[0112] Figure 18 The green curve in the figure is the polarization curve of PCNCF-piperazine prepared in the comparative example in the half cell; as can be seen from the figure, compared with PCNCF-SN in Example 1, the catalytic performance of PCNCF-piperazine is much lower than that of PCNCF-SN. The above results show that whether 2,2'-bithiophene is used or not determines whether the high-entropy intermetallic compound can be successfully synthesized.

[0113] Figure 17 The purple curve in the figure is the X-ray diffraction pattern of the catalyst PCNCF-thiourea-piperazine prepared in the comparative example. As can be seen from the figure, the diffraction peaks of the material are all split, there is serious phase segregation, and there is also no ordered diffraction peak, indicating that not any sulfur-containing ligand can play a similar role to 2,2'-bithiophene in the synthesis, and the thiourea ligand cannot effectively synthesize high-entropy intermetallic compounds. Figure 18The gold curve in Figure 1 is the polarization curve of the catalyst PCNCF-SN prepared in Example 1 in a half-cell. It can be seen from the figure that the catalyst PCNCF-SN has excellent catalytic performance. The red curve in Figure 1 is the polarization curve of the catalyst PCNCF-thiourea-piperazine prepared in Comparative Example 2 in a half-cell. It can be seen from the figure that the catalytic performance of PCNCF-thiourea-piperazine is much lower than that of PCNCF-SN in Example 1. The above results show that the use of 2,2'-bithiophene and its ligand effect have a direct impact on the performance of the catalyst, and further prove that 2,2'-bithiophene as a ligand and sulfur source is closely related to the successful synthesis of high-entropy intermetallic compounds.

[0114] Figure 17 The red curve in Figure 2 is the X-ray diffraction pattern of the catalyst PCNCF-1,2 dimethylimidazole-piperazine in the present comparative example. It can be found from the figure that the catalyst has ordered diffraction peaks, which shows that the use of nitrogen-containing ligand can synthesize high-entropy intermetallic compounds, but the diffraction peaks become abnormally sharp, which shows that the particle size of the synthesized catalyst increases sharply. It is known that the anchoring effect of N is not as good as S. This result further verifies that 2,2'-bithiophene as a ligand and sulfur source plays a key role in the synthesis. Figure 18 The blue curve in Figure 2 is the polarization curve of the catalyst PCNCF-1,2 dimethylimidazole-piperazine in the present comparative example in a half-cell; it can be seen from the figure that the catalytic performance of the high-entropy intermetallic compound PCNCF-1,2 dimethylimidazole-piperazine is much lower than that of PCNCF-SN in Example 1.

[0115] In summary, 2,2'-bithiophene plays a crucial role in the synthesis method of the present application, and cannot be replaced by any other sulfur-containing ligand, and its effect on the effective synthesis of high-entropy intermetallic compounds is much greater than that of nitrogen-containing ligands. In addition, the high-entropy intermetallic compound synthesized by using 2,2'-bithiophene as a ligand and sulfur source has better catalytic performance, which is mainly due to the stronger coordination effect of 2,2'-bithiophene, which better disperses the transition metal salt on the carbon carrier, and the anchoring effect brought by its as S source doping in the carbon carrier, further reducing the particle size of the catalyst, improving the activity and stability of the catalyst.

[0116] Comparative Example 4

[0117] The present comparative example is intended to verify the key role of acetone as a solvent in the synthesis.

[0118] The catalyst in the present comparative example is prepared by the same steps as in Example 1, named PCNCF-SN-methanol), the difference is that methanol is used instead of acetone as a solvent, and the other conditions are the same as in Example 1.

[0119] Figure 17The blue curve in the figure is the X-ray diffraction pattern of PCNCF-SN-methanol catalyst prepared in this comparative example. It can be found from the figure that the diffraction peak intensity of each crystal plane of the material is significantly reduced, and no ordered peak is observed, which indicates that methanol as a solvent cannot synthesize high-entropy intermetallic compounds. This result further indicates that acetone as a solvent plays a key role in the synthesis of effective high-entropy intermetallic compound materials.

[0120] Comparative Example 4 was tested in the polarization curve test process of half-cell with Example 1.

[0121] Figure 18 The curve represented by the purple dashed line in the figure is the polarization curve of PCNCF-SN-methanol catalyst prepared in this comparative example in the half-cell. It can be seen from the figure that the performance of PCNCF-SN-methanol catalyst is much lower than that of PCNCF-SN compared with PCNCF-SN in Example 1. The above results show that acetone as a solvent is directly related to whether high-entropy intermetallic compounds can be successfully synthesized.

[0122] Comparative Example 5

[0123] In order to further demonstrate the superiority of the PCNCF-SN catalyst material prepared in Example 1 in terms of synthesis process and performance, the synthesis conditions and electrochemical performance parameters of PCNCF-SN were compared with high-entropy intermetallic compounds synthesized by other methods reported in top journals in recent years, as shown in Table 2, PCNCF-SN as an oxygen reduction catalyst has excellent electrochemical performance, and the synthesis method has the characteristics of simple steps, easy operation, and low cost.

[0124] Table 3 Comparison of parameters of catalyst PCNCF-SN obtained in Example 1 with some high-entropy intermetallic compound materials published in the past five years

[0125]

[0126] Among them:

[0127] (1) Wang, Y.; Gong, N.; Liu, H.; Ma, W.; Hippalgaonkar, K.; Liu, Z.; Huang, Y. Ordering-Dependent Hydrogen Evolution and Oxygen Reduction Electrocatalysis of High-Entropy Intermetallic Pt4FeCoCuNi. Adv. Mater. 2023, 35 (28), 2302067. https: / / doi.org / 10.1002 / adma.202302067.

[0128] (2) Feng, G.; Ning, F.; Pan, Y.; Chen, T.; Song, J.; Wang, Y.; Zou, R.; Su, D.; Xia, D. Engineering Structurally Ordered High-Entropy Intermetallic Nanoparticles with High-Activity Facets for Oxygen Reduction in Practical Fuel Cells. J. Am. Chem. Soc. 2023, 145 (20), 11140-11150. https: / / doi.org / 10.1021 / jacs.3c00868.

[0129] (3) Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells | Science. https: / / www.science.org / doi / 10.1126 / science.abj9980 (accessed 2023-10-29).

[0130] (4) Hu, Y.; Xu, Z.; Guo, X.; Xiong, P.; Xu, C.; Chen, C.; Zhang, Q.; Wang, S.; Wu, T.-S.; Soo, Y.-L.; Li, M. M.-J.; Wang, D.; Zhu, Y. Hollow-Carbon Confinement Annealing: A New Synthetic Approach to Make High-Entropy Solid-Solution and Intermetallic Nanoparticles. Nano Lett. 2023, 23 (23), 10765-10771. https: / / doi.org / 10.1021 / acs.nanolett.3c02882.

[0131] (5) Zhang, Q.; Shen, T.; Song, M.; Wang, S.; Zhang, J.; Huang, X.; Lu, S.; Wang, D. High-Entropy L12-Pt(FeCoNiCuZn)3 Intermetallics for Ultrastable Oxygen Reduction Reaction. J. Energy Chem. 2023, 86, 158-166. https: / / doi.org / 10.1016 / j.jechem.2023.07.019.

[0132] (6) Chen, T.; Qiu, C.; Zhang, X.; Wang, H.; Song, J.; Zhang, K.; Yang, T.; Zuo, Y.; Yang, Y.; Gao, C.; Xiao, W.; Jiang, Z.; Wang, Y.; Xiang, Y.; Xia, D. An Ultrasmall Ordered High-Entropy Intermetallic with Multiple Active Sites for the Oxygen Reduction Reaction. J. Am. Chem. Soc. 2024, 146 (1), 1174-1184. https: / / doi.org / 10.1021 / jacs.3c12649.

[0133] From the comparison of typical works in the past five years in Table 3, it can be found that the synthesis method of the present application does not need to pretreat the carbon carrier or construct a special carbon carrier and template, and can be directly used for commercial carbon carriers, which is very key to the scale and commercialization of the method; at the same time, the catalyst synthesized by the present application has very small particle size, which is very outstanding compared with other methods, which can provide more catalytically active sites; in terms of oxygen reduction catalytic performance, it has higher activity and excellent stability, and can still maintain more than 60% activity after 100,000 cycles.

[0134] In summary, the present application overcomes the deficiencies in the prior art, provides a simple and convenient preparation method, and prepares S, N co-doped small nanometer size high-entropy intermetallic compounds by the method, which exhibits excellent activity and excellent stability in oxygen reduction reaction. Overall, the present application provides a new method for large-scale production of high-quality high-entropy intermetallic compound catalysts.

[0135] It should be noted that the above examples are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced, without departing from the spirit and scope of the present application, which should be covered in the scope of the present application.

Claims

1. A method for preparing a small nanoscale high-entropy intermetallic compound co-doped with S and N, characterized in that: include, Noble metal salts, transition metal salts, sulfur sources, and nitrogen sources are added to an organic solvent and stirred at room temperature. A carbon support is added and stirred at room temperature to obtain a mixture. The mixture is then ultrasonically treated to form a homogeneous mixture A. The noble metal salts include at least one of platinum salts, iridium salts, and palladium salts, and the transition metal salts are combinations of at least three of copper salts, nickel salts, cobalt salts, iron salts, manganese salts, and chromium salts. Mixture A was stirred at room temperature, and the organic solvent was evaporated by heating to form a black viscous paste B. B was transferred to a vacuum oven to dry, and the intermediate product was obtained. The intermediate product was annealed at high temperature in a reducing atmosphere to obtain S,N co-doped small nano-sized high-entropy intermetallic compounds. The sulfur source includes 2,2'-bisthiophene, and the organic solvent includes acetone. The S,N co-doped small nanoscale high-entropy intermetallic compounds include carbon supports containing S and N co-doped heteroatom sites, metal single-atom sites, and high-entropy intermetallic compounds loaded on carbon substrates. The S,N co-doped small nano-sized high-entropy intermetallic compound comprises high-entropy intermetallic compound particles composed of more than 5 metal elements. The particle size of the S,N co-doped small nano-sized high-entropy intermetallic compound particles is 2~5 nm.

2. The preparation method according to claim 1, characterized in that: The platinum salt is platinum acetylacetonate, the iridium salt is iridium acetylacetonate, and the palladium salt is palladium acetylacetonate.

3. The preparation method according to claim 1 or 2, characterized in that: The copper salt is copper acetylacetone, the nickel salt is nickel acetylacetone, the cobalt salt is cobalt acetylacetone, the iron salt is iron acetylacetone, the manganese salt is manganese acetylacetone, and the chromium salt is chromium acetylacetone.

4. The preparation method according to claim 3, characterized in that: The nitrogen source is any one of melamine, pipemidic acid, aminoantipyrine, triaminopyrazole, and pyridine.

5. The preparation method according to claim 1 or 4, characterized in that: The carbon support is at least one of carbon black, carbon nanotubes, and Ketjen black.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the noble metal salt to the transition metal salt is (6~8):5; the mass ratio of the noble metal salt to the carbon support is (3~4):10; and the mass ratio of the sulfur source, nitrogen source, and carbon support is 1~2:1~2:1~12.

7. The preparation method according to claim 1 or 6, characterized in that: The addition of carbon support and stirring at room temperature yields a mixture, wherein the stirring time is 30-60 min; the mixture is ultrasonically treated to form a homogeneous mixture A, wherein the ultrasonic treatment time is 1-4 h; the organic solvent is evaporated by heating, wherein the solvent evaporation temperature is 70°C and the treatment time is 0.5-1 h; and B is transferred to a vacuum oven for drying, wherein the drying temperature is 60°C and the drying time is 12-24 h.

8. The preparation method according to claim 1, characterized in that: The high-temperature annealing atmosphere is 10% H2 / Ar, the annealing heating rate is 3~5℃ / min, the annealing temperature is 800~1000℃, and the annealing time is 2~4h.

9. S, N co-doped small nanoscale high-entropy intermetallic compounds prepared by any of the preparation methods described in claims 1 to 8.

10. The application of the S,N co-doped small nano-sized high-entropy intermetallic compound of claim 9 in the oxygen reduction reaction at the cathode of a proton exchange membrane fuel cell.

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