CN113937305A - Graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst and preparation method thereof - Google Patents

Graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst and preparation method thereof Download PDF

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CN113937305A
CN113937305A CN202111164570.0A CN202111164570A CN113937305A CN 113937305 A CN113937305 A CN 113937305A CN 202111164570 A CN202111164570 A CN 202111164570A CN 113937305 A CN113937305 A CN 113937305A
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platinum
cobalt
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oxygen reduction
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夏宝玉
沙明亮
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9041—Metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • H01M4/9083—Catalytic material supported on carriers, e.g. powder carriers on carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
    • H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst and a preparation method thereof. The preparation method comprises the following steps: (1) uniformly mixing a cobalt metal salt solution and an organic ligand solution, then adding a platinum metal salt, uniformly mixing, and carrying out vacuum drying to obtain precursor powder; (2) and uniformly mixing the precursor powder and the alkali metal salt powder, heating, annealing and carrying out acid treatment to obtain the graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst. According to the invention, the platinum nano alloy coated in the Co-Nx/C doped modified carbon nano sheet is prepared by a simple molten salt synthesis method, and the catalyst prepared by the method is subjected to concerted catalysis through the comprehensive action of the platinum alloy, a non-platinum group metal active site (Co-N4) and a heteroatom doped modified carbon nano sheet, has good oxygen reduction activity and durability in an acidic medium, and can meet the practical application of various energy conversion technologies.

Description

Graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst and preparation method thereof
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to a graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst and a preparation method thereof.
Background
The Oxygen Reduction Reaction (ORR) is the core reaction of numerous electrochemical energy technologies, especially polymer electrolyte membrane fuel cells and metal air cells. However, ORR is a huge impediment to the widespread use of many renewable energy technologies due to the complex multiple electronic steps and slow reaction kinetics. Platinum nanoparticles supported on amorphous carbon black (Pt/C) are a very representative commercial ORR catalyst. However, Pt/C has poor catalytic performance, especially durability, and cannot meet the requirements of large-scale application. Meanwhile, the high cost of Pt/C catalysts is also one of the important reasons limiting the commercialization of fuel cells and many electrochemical energy technologies. Therefore, the search for an inexpensive cathode ORR catalyst with high activity and high stability is essential for the development and popularization of new energy technology.
In this regard, researchers have adopted various strategies to reduce the amount of platinum and improve its catalytic performance, which has contributed to the acceleration of the large-scale commercialization of platinum-based catalysts. Alloying platinum with transition metals for surface electronic structure modification has become an effective strategy to improve ORR catalytic activity and reduce catalyst cost. The transition metal doped into the platinum lattice can optimize the binding strength of the platinum-oxygen intermediate by synergistic effects (assembly, organic ligands and strain). In addition, the unique nano structure can obviously expose catalytic active sites, and improve the mass transfer speed in the reaction process, thereby improving the ORR electro-catalysis performance. In recent years, researchers have reported different kinds of platinum-based alloys and intermetallic compounds having excellent activity and durability.
The conventional amorphous carbon black is used only as a support for supporting platinum nanoparticles. However, the modification of the carbon support can provide a dual function, which can not only serve as an anchor site for the catalyst nanoparticles, but also have ORR activity, which will create some additional active sites, thereby improving the overall performance of the catalyst. Thus, upgrading of carbon supports can bring numerous advantages such as dispersing catalyst nanoparticles, creating more reaction channels, and introducing additional active sites through defect engineering and heteroatom doping. In particular, metal-organic framework (MOF) -derived nanocarbons that can uniformly anchor catalyst particles are considered as a promising support alternative to conventional carbon black due to the high number of exposed active sites, high electrochemical surface area (ECSA) and strong corrosion resistance. Recently, PtCo core-shell nanoparticles embedded in MOF derived nanocarbons exhibited excellent ORR activity because they were rich in Co-Nx/C sites and Co @ graphene as well as some single atom sites and ultra-low platinum loading (2.72 wt.%). In addition, there is currently a large body of work on support upgrading and concerted catalysis revealing the important role of carbon supports for enhancing ORR catalysis.
In addition, platinum monatomic catalysts (SACs) supported on defective carbon can exhibit an ultra-high platinum atom utilization in ORR. Obviously, the utilization rate of platinum in SACs reaches the highest, and the electrochemical activity can be obviously improved. However, higher platinum loading SACs cannot meet the long life requirement in energy conversion devices due to agglomeration of nanoparticles. In contrast, heteroatom-doped three-dimensional nanostructures have strong anchor sites, unique anisotropy, high flexibility and conductivity, and the supported platinum is more stable.
In summary, many efforts have been made to design platinum alloy catalysts and upgrade the carriers for ORR in various energy conversion technologies, but the existing catalysts still have problems such as complicated preparation technology, poor stability, and mass production.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst, and a platinum nano alloy coated in Co-Nx/C doped modified carbon nanosheets is prepared by a simple molten salt synthesis method, and is subjected to concerted catalysis through the comprehensive action of the platinum alloy, non-platinum metal active sites (Co-N4) and heteroatom doped modified carbon nanosheets, so that the prepared catalyst has good ORR activity and durability in an acid medium, and can meet the practical application of various energy conversion technologies. The detailed technical scheme of the invention is as follows.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a method for preparing a graphitic carbon-coated platinum-cobalt alloy oxygen-reduction electrocatalyst, comprising the steps of:
(1) uniformly mixing a cobalt metal salt solution and an organic ligand solution, then adding a platinum metal salt, uniformly mixing, and carrying out vacuum drying to obtain precursor powder;
(2) and uniformly mixing the precursor powder and the alkali metal salt powder, heating, annealing and carrying out acid treatment to obtain the graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst.
Preferably, the heating temperature in step (2) is 650-950 ℃.
Preferably, the heating time in step (2) is 2 to 6 hours.
Preferably, the alkali metal salt in step (2) includes KCl, NaCl, KNO3、LiCl、NaN3And LiNO3At least one of (1).
Preferably, the alkali metal salt is LiCl and KCl, and the mass ratio of the LiCl to the KCl is (1-2): 4.
preferably, the platinum metal salt is one of platinum acetylacetonate, chloroplatinic acid and potassium chloroplatinate; the cobalt metal salt is one of cobalt nitrate, cobalt sulfate and cobalt chloride; the organic ligand is one of polyvinyl pyridine, 2-methylimidazole and trimethyl ammonium bromide.
Preferably, the non-platinum transition metal salt is added at the same time as the platinum metal salt is added in the step (1).
Preferably, the non-platinum transition metal salt is at least one of cobalt chloride, iron acetate, cobalt nitrate, palladium chloride, cobalt acetate, copper chloride, niobium chloride, lead nitrate, tin oxide, molybdenum chloride, and nickel nitrate.
Preferably, the acid treatment is acid washing with nitric acid or sulfuric acid for 24 to 48 hours.
According to another aspect of the present invention there is provided a graphitic carbon-coated platinum-cobalt alloy oxygen-reducing electrocatalyst prepared according to the preparation method hereinbefore described.
The invention has the following beneficial effects:
(1) according to the invention, the platinum nano alloy coated in the Co-Nx/C doped modified carbon nano sheet is prepared by a simple molten salt synthesis method, and the catalyst prepared by the method is subjected to concerted catalysis through the comprehensive action of the platinum alloy, a non-platinum group metal active site (Co-N4) and a heteroatom doped modified carbon nano sheet, has good ORR activity and durability in an acidic medium, and can meet the practical application of various energy conversion technologies.
(2) The preparation method comprises the steps of mixing platinum metal salt, transition metal salt and ZIF, reacting at a certain temperature for a certain time to prepare a precursor, mixing with an alkali metal salt in a proper proportion, fully and manually grinding, annealing at a high temperature under an optimized condition to obtain the morphology of the ultrathin graphite carbon nanosheet, washing with deionized water, and performing acid etching in strong acid with a specific concentration to obtain the final catalyst. The synthesis method is simple and efficient, inert gas protection is not needed in the synthesis process, the use of noble metal platinum is reduced, large-scale production and preparation can be realized, and the industrial cost of the catalyst can be effectively reduced.
(3) The coating synthesized by the invention is rich in Co-N4The platinum nanoalloy catalyst in graphitic carbon nanosheets has Pt and non-Pt (Co-N)4) The dual ORR active sites greatly improve the utilization rate of platinum, have excellent stability which is 10-40 times that of a commercial Pt/C catalyst, have the advantages of excellent corrosion resistance and cycle stability and high electrocatalytic activity, are suitable choices for large-scale industrial production, and have important significance for promoting the commercialization process of various energy conversion devices.
Drawings
FIG. 1 is a schematic diagram of the synthesis principle of the graphite carbon-coated platinum-cobalt alloy of the present invention.
Figure 2 is an X-ray diffraction pattern of a graphitic carbon-coated platinum cobalt alloy prepared according to example 3, example 7, comparative example 1 and commercial Pt/C according to comparative example 2.
Figure 3 is a raman plot of the graphitic carbon-coated platinum-cobalt alloys prepared in examples 1, 2, 3 and 4.
Fig. 4 is a transmission electron microscope image of a graphitic carbon-coated platinum cobalt alloy prepared according to example 3, wherein a in fig. 4 is an image of 2 μm in size and b is an image of 10 nm in size.
Figure 5 is a graph of the ORR activity tests of the graphitic carbon-coated platinum cobalt alloys prepared in examples 3 and 7 with the commercial Pt/C catalyst of comparative example 2.
Figure 6 is a graph of the cycling stability tests of the graphitic carbon-coated platinum cobalt alloys prepared in examples 3 and 7 and the commercial Pt/C of comparative example 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Examples
Example 1
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NGNS: 500mg of the precursor, 2g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 650 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 2
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NGNS: 500mg of the precursor, 2g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 750 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 3
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NGNS: 500mg of the precursor, 2g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 850 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 4
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NGNS: 500mg of the precursor, 2g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 950 ℃ under an Ar gas atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 5
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NGNS: 500mg of the precursor, 4g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 850 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 6
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NGNS: 500mg of the precursor, 6g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 850 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 7
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2The solution was stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NC: 500mg of the precursor was ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 850 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Example 8
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparing a precursor: 3mmol (873mg)Cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed, stirred continuously for 30 minutes, and then 30mM H was added2PtCl6·6H2O solution and 30mM palladium chloride solution, and stirred for 4 hours. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of PtCo @ NC: 500mg of the precursor was ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 850 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Comparative example 1
A graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is prepared by the following method:
(1) preparation of ZIF: 3mmol (873mg) of cobalt nitrate hexahydrate and 12mmol (984mg) of 2-methylimidazole were dissolved in 20mL of deionized water, respectively, to obtain clear solutions. The two solutions were mixed and stirred continuously for 30 minutes. The resulting violet-blue precipitate was collected by centrifugation at 10,000rpm for 5 minutes and washed 3 times with deionized water before vacuum drying at 70 ℃ overnight.
(2) Preparation of Co @ NGNS: 500mg of ZIF, 2g of LiCl and 8g of KCl were ground in a mortar and placed in a quartz boat, and then transferred to a tube furnace. The sample was heated at 850 ℃ under an Ar atmosphere for 4 hours. After natural cooling to room temperature, the resulting product was washed with deionized water and then washed with 0.5M HNO3Treated with medium acid for 36 hours, washed with deionized water, and dried at 60 ℃ for 6 hours.
Comparative example 2
Commercial Pt/C catalyst, Hisec3000 platinum carbon catalyst from Johnson Matthey, USA.
FIG. 1 is a schematic diagram of the synthesis principle of the graphite carbon-coated platinum-cobalt alloy of the present invention.
As shown in figure 1, cobalt metal salt and organic ligand are dissolved, platinum metal salt is added, and a precursor PtCo @ ZIF is obtained after vacuum drying; and uniformly mixing the precursor PtCo @ ZIF and alkali metal salt powder, heating, annealing and carrying out acid treatment to obtain the catalyst.
Figure 2 is an X-ray diffraction pattern of a graphitic carbon-coated platinum cobalt alloy prepared according to example 3, example 7, comparative example 1 and commercial Pt/C according to comparative example 2.
As can be seen from fig. 2, the diffraction peak of the graphitic carbon-coated platinum-cobalt alloy is slightly shifted positively compared to the commercial Pt/C, indicating successful doping of cobalt into the lattice of platinum.
Figure 3 is a raman plot of the graphitic carbon-coated platinum-cobalt alloys prepared in examples 1, 2, 3 and 4.
As can be seen from fig. 3, the presence of the G peak indicates that graphitic carbon is formed, and the degree of graphite carbonization increases with increasing temperature.
Fig. 4 is a transmission electron microscope image of a graphitic carbon-coated platinum cobalt alloy prepared according to example 3, wherein a in fig. 4 is an image of 2 μm in size and b is an image of 10 nm in size.
As can be seen from fig. 4, the prepared catalyst has a uniform lamellar structure, and the platinum-cobalt alloy is encapsulated in the graphitic carbon, which can weaken the dissolution of non-noble metals under acidic conditions, thereby improving the stability of the catalyst.
Figure 5 is a graph of the ORR activity tests of the graphitic carbon-coated platinum cobalt alloys prepared in examples 3 and 7 with the commercial Pt/C catalyst of comparative example 2.
As is clear from FIG. 5, the mass activity and specific activity of the graphite carbon-coated platinum-cobalt alloy obtained in example 3 were 1.3A mgPt -1And 1.7A cm-2Much higher than commercial Pt/C. This demonstrates that the graphitic carbon-coated platinum-based alloy prepared by this method has excellent ORR catalytic activity, further demonstrating the feasibility of this method to obtain high performance catalysts.
Figure 6 is a graph of the cycling stability tests of the graphitic carbon-coated platinum cobalt alloys prepared in examples 3 and 7 and the commercial Pt/C of comparative example 2.
As can be seen from fig. 6, the mass activity of the graphitic carbon-coated platinum-cobalt alloy prepared from example 3 decayed only 20% after 30000 cycles, while the commercial Pt/C decayed 70%. The doped nitrogen provides a strong anchor site for the cobalt, forming a more stable Co-N4 site to prevent cobalt dissolution and aggregation. On the other hand, the graphite carbon layer protects the platinum-based alloy from dissolving, and the durability of the catalyst is further improved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A preparation method of a graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst is characterized by comprising the following steps:
(1) uniformly mixing a cobalt metal salt solution and an organic ligand solution, then adding a platinum metal salt, uniformly mixing, and carrying out vacuum drying to obtain precursor powder;
(2) and uniformly mixing the precursor powder and the alkali metal salt powder, heating, annealing and carrying out acid treatment to obtain the graphite carbon-coated platinum-cobalt alloy oxygen reduction electrocatalyst.
2. The method for preparing a catalyst according to claim 1, wherein the heating temperature in the step (2) is 650-950 ℃.
3. The method for preparing a catalyst according to claim 2, wherein the heating time in the step (2) is 2 to 6 hours.
4. The method for preparing a catalyst according to claim 2 or 3, wherein the alkali metal salt in the step (2) comprises KCl, NaCl, KNO3、LiCl、NaN3And LiNO3At least one of (1).
5. The method for preparing the catalyst according to claim 4, wherein the alkali metal salt is LiCl and KCl, and the mass ratio of the LiCl to the KCl is (1-2): 4.
6. the method for preparing a catalyst according to claim 1, wherein the platinum metal salt is one of platinum acetylacetonate, chloroplatinic acid, and potassium chloroplatinate; the cobalt metal salt is one of cobalt nitrate, cobalt sulfate and cobalt chloride; the organic ligand is one of polyvinyl pyridine, 2-methylimidazole and trimethyl ammonium bromide.
7. The method for preparing a catalyst according to any one of claims 1 to 6, wherein a non-platinum transition metal salt is added simultaneously with the addition of the platinum metal salt in step (1).
8. The method for preparing a catalyst according to claim 7, wherein the non-platinum transition metal salt is at least one of cobalt chloride, iron acetate, cobalt nitrate, palladium chloride, cobalt acetate, copper chloride, niobium chloride, lead nitrate, tin oxide, molybdenum chloride, and nickel nitrate.
9. The method for preparing a catalyst according to claim 1, wherein the acid treatment is an acid washing with nitric acid or sulfuric acid for 24 to 48 hours.
10. A graphitic carbon-coated platinum-cobalt alloy oxygen-reduction electrocatalyst characterized by being prepared according to the preparation method of any one of claims 1 to 9.
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