CN113363504B - Preparation method of platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst - Google Patents

Preparation method of platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst Download PDF

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CN113363504B
CN113363504B CN202010679218.XA CN202010679218A CN113363504B CN 113363504 B CN113363504 B CN 113363504B CN 202010679218 A CN202010679218 A CN 202010679218A CN 113363504 B CN113363504 B CN 113363504B
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platinum
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doped graphene
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CN113363504A (en
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黄华杰
严敏敏
沈斌锋
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Hohai University HHU
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    • 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
    • H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
    • H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
    • 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
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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
    • H01M4/90—Selection of catalytic material
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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
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    • 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
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1009—Fuel cells with solid electrolytes with one of the reactants being liquid, solid or liquid-charged
    • H01M8/1011—Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC]
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Abstract

The invention provides a preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, and relates to the field of electrode catalysts. According to the invention, the platinum, the manganese cobaltate and the nitrogen-doped graphene are compounded, so that the electrocatalytic performance of the manganese cobaltate and the platinum can be cooperatively exerted, the self-supporting effect of the graphene can be fully utilized, and the prepared three-dimensional composite catalyst has the advantages of large specific surface area, more active sites, good cycle stability and excellent catalytic performance.

Description

Preparation method of platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst
Technical Field
The invention relates to a preparation method of an electrode catalyst, and particularly relates to a preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst.
Background
In the face of increasingly aggravated energy crisis and environmental pollution, environmental protection, energy conservation and emission reduction become important subjects facing the current society. The development and utilization of high-efficiency and clean energy have important significance for the sustainable development of the society. The direct methanol fuel cell is a new energy technology with application prospect, and the popularization and the application of the direct methanol fuel cell not only can effectively relieve the dependence of the current social economy on fossil fuel, but also can greatly reduce the damage to the ecological environment in the energy production and consumption processes. A large number of research results show that the noble metal platinum has high catalytic activity on methanol oxidation reaction and is often used as an electrode catalyst material for new energy technology. However, the platinum has limited reserves in nature and high price, and is also very easy to generate poisoning phenomenon in the catalytic process to cause activity reduction, which greatly restricts the large-scale commercial application of the platinum in the catalytic field. Therefore, a novel composite platinum-based catalyst which has excellent performances such as high catalytic activity, high toxicity resistance and the like and is relatively cheap is sought, and the composite platinum-based catalyst has great significance for economic development and environmental improvement of the current society.
As a novel carbon material, graphene has the advantages of large specific surface area, high conductivity, high mechanical strength, electrochemical stability and the like, and can be used as an ideal conductive additive. However, the toxicity resistance and stability of the graphene-based catalyst need to be improved in the actual use process, and the graphene-based catalyst is prone to irreversible agglomeration and stacking in both the preparation and actual use processes, which may cause a part of the reactive sites to be covered and reduce the catalytic efficiency, so that it is necessary to add a material with excellent catalytic performance and stable electrochemical performance to increase the reactive centers exposed by the graphene material and improve the catalytic efficiency. In recent years, transition bimetallic oxide manganese cobaltate with a spinel structure has been widely researched due to the advantages of abundant resources, low cost, environmental friendliness and the like. In particular, manganese cobaltate has excellent electrochemical activity and conductivity, and shows certain electrocatalytic activity on methanol oxidation. At the same time, the hydroxyl species adsorbed on the manganese cobaltate surface help to promote the removal of intermediates in the methanol oxidation process. Up to now, noble metals are directly loaded on three-dimensional nitrogen-doped graphene or transition metal oxides are utilized to modify the nitrogen-doped graphene to obtain electrode catalysts with higher activity (ZHOU Y-G, CHEN J-J, WANG F-B, et al].Chem Commun,2010,46(32):5951.LIANG Y, Li Y,WANG H,et al.Co3O4nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction[J].Nature Materials,2011,10(10):780-6.JIAO J,WEN L Q,WANG Z H,et al. Highly Sensitive Sensor Based on Pt@MnO2/rGO Nanosheets as a Platform for Real-time Monitoring Cellular ROS and its Application in Diverse Cancers[J]J Electrochem Soc,2020, 167(6): 8.). However, the electrochemical performance of the electrode catalyst prepared by the above method is still to be improved. At present, no research is reported on constructing a three-dimensional composite carrier by adopting manganese cobaltate nanocrystals and nitrogen-doped graphene and loading platinum nanoparticles by using the three-dimensional composite carrier.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst; according to the invention, the platinum, the manganese cobaltate and the nitrogen-doped graphene are compounded, so that the Faraday electrochemical property of the manganese cobaltate and the electrocatalytic property of the platinum can be fully utilized, the self-supporting effect of the graphene and the intercalation effect of the manganese cobaltate can be fully utilized, the nano-sheets are not accumulated and agglomerated and tend to be uniformly dispersed, the manganese cobaltate and platinum nano-crystal grains are more uniformly distributed and have smaller sizes, the active sites are effectively increased, the transmission rate of electrons is higher, and the catalytic activity of the composite electrode catalyst is improved.
A preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing a graphene oxide dispersion liquid;
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, uniformly stirring to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 1-20: 1-20, wherein the addition amount of nitrogen elements in the ammonia water and the addition amount of graphene oxide are 1: 1 to 100;
s3, carrying out hydrothermal reaction on the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 to obtain a hydrogel-like product, then dialyzing, washing with water, and freeze-drying to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene in the step S3, performing hydrothermal reaction, performing centrifugal washing, and performing freeze drying to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the platinum in the platinum salt and the manganese cobaltate nanocrystal/nitrogen-doped graphene binary composite is 1: 1 to 20.
Graphene oxide is ultrasonically stripped to generate a two-dimensional single-layer or few-layer graphene oxide nanosheet, and then the graphene oxide nanosheet is subjected to constant-temperature stirring and hydrothermal reaction with cobalt salt, manganese salt and ammonia water, and ammonia water is dissociated to generate NH4 +Ions can easily enter between graphene oxide layers to cause expansion of different degrees in the c-axis direction of the graphene oxide layers so as to increase the interlayer spacing of the graphene, and meanwhile, under the heating condition, nitrogen atoms are doped into a graphene atom array and are used as nucleation sites of cobalt salt and manganese salt together with a large number of oxygen-containing functional groups contained in the graphene oxide, so that the nucleation growth of the manganese cobaltate is promoted, and manganese cobaltate nanoparticles are effectively dispersed; and then adding platinum salt, adsorbing platinum ions on the surface of the nitrogen-doped graphene through the ion exchange effect of oxygen-containing functional groups on the surface of the graphene, and reducing the platinum ions into platinum nanoparticles loaded on the surface of the nitrogen-doped graphene sheet layer through constant-temperature stirring and hydrothermal reaction to obtain the three-dimensional composite catalyst with high electrocatalysis performance.
Adopt above-mentioned technical scheme: the single-layer or few-layer graphene oxide nanosheets are used as building elements and are assembled into a highly-wrinkled three-dimensional self-supporting structure from bottom to top, and oxygen-containing functional groups rich on the surface of the three-dimensional self-supporting structure are used as load sites of the platinum and the manganese cobaltate nanocrystal, so that the dispersion of the manganese cobaltate and platinum nanoparticles is greatly promoted, the manganese cobaltate and platinum nanocrystal are prevented from being aggregated and grown, the size of the nanocrystal is small, the number of active sites in unit area is large, and the electrochemical performance is improved. And secondly, the interlayer spacing of the nitrogen-doped graphene is increased, and meanwhile, the manganese cobaltate nanocrystal can be used as an effective intercalation material, so that the interlayer spacing of the graphene is further increased, and the stacking of the nitrogen-doped graphene is inhibited. The synergistic effect can enable the gaps among the overlapped graphene oxide nanosheets to be mutually communicated to form a microporous network, and the microporous network has a larger internal space, so that the dispersion among the nanosheets is promoted, more active sites are exposed, the specific surface area is large, the electrolyte can be allowed to enter to the maximum extent, smooth channels are provided for the transmission of electrons and the permeation of the electrolyte into the catalyst, and the active sites are ensured to be fully contacted with a reaction medium. In addition, the manganese cobaltate nanoparticles in the catalyst have certain methanol oxidation activity, can promote the activation and decomposition of water under reduced potential to generate oxygen-containing substances, and are beneficial to oxidizing and removing toxic carbon-containing species strongly adsorbed on the surface of platinum, so that active sites on the surface of the platinum are released, and the catalytic activity of the catalyst is further improved after the manganese cobaltate nanoparticles are hybridized with nitrogen-doped graphene and platinum nanoparticles.
Further, in step S2, the addition amount of the graphene oxide and the manganese cobaltate is 1-10: 1-10, wherein the addition amount of nitrogen elements and graphene oxide in the ammonia water is 1: 20.
further, in step S2, the addition amount of the graphene oxide and the manganese cobaltate is 1: 2, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 20.
further, in step S4, the addition amount of the platinum in the platinum salt and the manganese cobaltate nanocrystal/nitrogen-doped graphene binary compound is 1: 3 to 10.
Further, in step S4, the addition amount of the platinum in the platinum salt and the manganese cobaltate nanocrystal/nitrogen-doped graphene binary compound is 1: 5.
further, in step S2, the cobalt salt is cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt acetate, or cobalt chloride; the manganese salt is manganese nitrate, manganese acetate, manganese sulfate, manganese acetate or manganese chloride. The method is not limited to the cobalt salt and the manganese salt provided by the invention, as long as manganese cobaltate can be generated in the titanium carbide nanosheet dispersion liquid to realize uniform growth of manganese cobaltate nanocrystal particles on the graphene oxide lamella.
Further, in step S1, the concentration of the graphene oxide dispersion liquid is 0.1-5 g/L.
Further, in step S2, the stirring conditions are: magnetic stirring is carried out for 1 to 24 hours at the temperature of between 0 and 100 ℃.
Further, in step S3, the hydrothermal reaction conditions are: the reaction time is 2-48h at 100-200 ℃, the dialysis water washing time is 1-10 times, and the drying pressure during freeze drying is 10-200 Pa.
Further, in step S4, the hydrothermal reaction conditions are: the reaction time is 2-48h at 100-200 ℃, the centrifugal water washing time is 1-10 times, and the drying pressure during freeze drying is 10-200 Pa.
The invention achieves the following beneficial technical effects:
1. according to the preparation method of the platinum/manganese cobaltate nanocrystalline/nitrogen-doped graphene three-dimensional composite electrode catalyst, the prepared electrode catalyst is assembled into a highly-wrinkled three-dimensional self-supporting structure from bottom to top, the specific surface area is large, the number of catalytic active sites is large, the stability is good, and the catalytic performance of the composite electrode catalyst is excellent; the composite electrode catalyst has better application prospect and economic benefit in the fields of methanol fuel cells and the like.
2. The composite electrode catalyst has the advantages that the platinum, the manganese cobaltate and the nitrogen-doped graphene are compounded, so that the Faraday electrochemical property of the manganese cobaltate and the electrocatalytic property of the platinum can be fully utilized, the self-supporting effect of the graphene and the intercalation effect of the manganese cobaltate can be fully utilized, the nanosheets are not accumulated and agglomerated and tend to be uniformly dispersed, the manganese cobaltate and platinum nanocrystalline grains are more uniformly distributed and have smaller sizes, the active sites are effectively increased, the transmission rate of electrons is higher, and the catalytic activity of the composite electrode catalyst is improved.
3. The manganese cobaltate and graphene oxide are low in price, rich in sources, low in cost, simple and controllable in preparation method, good in repeatability, beneficial to large-scale production and high in practical value.
Drawings
FIG. 1 is a schematic flow chart of a preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst according to the present invention;
fig. 2 is an X-ray diffraction (XRD) spectrum of the graphene oxide nanosheet, platinum/graphene and platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene composite electrode catalyst prepared by the method of embodiment 3 of the present invention;
fig. 3 is a field emission scanning electron microscope (FE-SEM) photograph of the platinum/manganese cobaltate nanocrystal/nitrogen doped graphene three-dimensional composite electrode catalyst prepared by the method of example 3 (fig. a, B) of the present invention and comparative examples 2, 3 (fig. C, D);
fig. 4 is a Transmission Electron Microscope (TEM) photograph of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst prepared by the method of example 3 of the present invention;
fig. 5 is a nitrogen adsorption/desorption graph of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst prepared by the method in embodiment 3 of the invention;
FIG. 6 shows a Pt/Mn cobaltate nanocrystal/N-doped graphene three-dimensional composite electrode catalyst (Pt/MnCo) prepared by the method of embodiment 3 of the present invention2O4-NG), platinum/nitrogen doped graphene (Pt/NG), platinum/graphene (Pt/G) and platinum/carbon (Pt/C) catalysts electrochemically active area (panel a) and cyclic voltammogram (panel B);
fig. 7 is a long-range stability test chart of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst prepared by the method in embodiment 3 of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is obvious that the described embodiments are only some embodiments of the present invention, not all 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.
As shown in fig. 1, a preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing 0.1-5g/L graphene oxide dispersion liquid: ultrasonically stripping graphene oxide in water at 0-60 ℃ for 0.5-10h to obtain a graphene oxide dispersion liquid; since the prior art has reported a lot of reports on the dispersion degree of graphene oxide by ultrasonic temperature and time, the application is not repeated, and room-temperature ultrasonic stripping is preferably performed for 5 hours in the following embodiments as the preparation condition of the invention;
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, and magnetically stirring for 1-24 hours at 0-100 ℃ to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 1-20: 1-20, wherein the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 1-100;
the cobalt salt is any one or more of cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt acetate or cobalt chloride; the manganese salt is any one or more of manganese nitrate, manganese acetate, manganese sulfate, manganese acetate or manganese chloride; the cobalt salt and the manganese salt can provide cobalt ions and manganese ions, and can produce similar effects, the invention is not discussed, and the following examples take cobalt sulfate and manganese sulfate as examples;
s3, placing the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 under the hydrothermal condition of 100-200 ℃ for reaction for 2-48h, then dialyzing and washing for 1-10 times, and then freeze-drying under the pressure condition of 10-200Pa to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene obtained in the step S3, carrying out hydrothermal reaction for 2-48h at the temperature of 100-200 ℃, then carrying out centrifugal washing for 1-10 times, and then carrying out freeze drying under the pressure condition of 10-200Pa to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the platinum in the platinum salt and the manganese cobaltate nanocrystal/nitrogen-doped graphene binary composite is 1: 1 to 20.
Meanwhile, through earlier tests, the stirring temperature and time, the hydrothermal reaction temperature and time and the like in the steps S2-S4 have less influence on the shape and size of the platinum/manganese cobaltate nanocrystal when the stirring temperature and time, the hydrothermal reaction temperature and time and the like are changed within the range of the application, and the invention is not separately discussed.
Example 1
The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing 0.1g/L graphene oxide dispersion liquid:
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, and magnetically stirring the mixture at a constant temperature of 0 ℃ for 1 hour to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 1: 20, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 100;
s3, placing the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 under a 100 ℃ hydrothermal condition for reaction for 6 hours, then dialyzing and washing for 2 times, and then freeze-drying under a pressure of 10Pa to remove moisture to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene obtained in the step S3, carrying out hydrothermal reaction for 4h at 100 ℃, then carrying out centrifugal water washing for 1 time, and then carrying out freeze drying under the pressure condition of 10Pa to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the binary composite of platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene in the platinum salt is 1: 20.
example 2
The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing 2g/L graphene oxide dispersion liquid:
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, and magnetically stirring the mixture at a constant temperature of 80 ℃ for 10 hours to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 1: 10, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 20;
s3, placing the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 under a hydrothermal condition of 180 ℃ for 24 hours, then dialyzing and washing for 5 times, and then freeze-drying under a pressure of 25Pa to remove moisture to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene obtained in the step S3, carrying out hydrothermal reaction for 24 hours at 120 ℃, then carrying out centrifugal water washing for 1 time, and then carrying out freeze drying under the pressure condition of 10Pa to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the binary composite of platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene in the platinum salt is 1: 10.
example 3
The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing 2g/L graphene oxide dispersion liquid:
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, and magnetically stirring the mixture at a constant temperature of 80 ℃ for 10 hours to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 1: 2, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 20;
s3, placing the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 under a hydrothermal condition of 180 ℃ for 24 hours, then dialyzing and washing for 5 times, and then freeze-drying under a pressure of 25Pa to remove moisture to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene obtained in the step S3, carrying out hydrothermal reaction for 24 hours at 120 ℃, then carrying out centrifugal water washing for 1 time, and then carrying out freeze drying under the pressure condition of 10Pa to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the binary composite of platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene in the platinum salt is 1: 5.
example 4
The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing 2g/L graphene oxide dispersion liquid:
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, and magnetically stirring the mixture at a constant temperature of 80 ℃ for 10 hours to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 10: 1, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 20;
s3, placing the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 under a hydrothermal condition of 180 ℃ for 24 hours, then dialyzing and washing for 5 times, and then freeze-drying under a pressure of 25Pa to remove moisture to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene obtained in the step S3, carrying out hydrothermal reaction for 24 hours at 120 ℃, then carrying out centrifugal water washing for 1 time, and then carrying out freeze drying under the pressure condition of 10Pa to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the binary composite of platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene in the platinum salt is 1: 3.
example 5
The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst comprises the following steps:
s1, preparing 5g/L graphene oxide dispersion liquid:
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, and magnetically stirring the mixture at a constant temperature of 100 ℃ for 24 hours to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 20: 1, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 1;
s3, placing the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 under a 200 ℃ hydrothermal condition for reaction for 48 hours, then dialyzing and washing for 10 times, and then freeze-drying under a 200Pa pressure condition to remove moisture to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene obtained in the step S3, carrying out hydrothermal reaction for 48h at 200 ℃, then carrying out centrifugal water washing for 10 times, and then carrying out freeze drying under the pressure of 200Pa to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene binary composite in the platinum salt is 1: 1.
comparative example 1
The difference between the comparative example 1 and the example 3 is that in the step S2, the addition amount of the graphene oxide and the manganese cobaltate is 1: 30.
comparative example 2
The difference between the comparative example 2 and the example 3 is that in the step S2, the addition amount of the graphene oxide and the manganese cobaltate is 30: 1.
comparative example 3
The difference between the comparative example 3 and the example 3 is that the addition amount of the platinum and the manganese cobaltate nanocrystal/nitrogen-doped graphene binary compound in the platinum salt is 1: 25.
comparative example 4
The difference between the comparative example 4 and the example 3 is that the nickel sulfate is replaced by the same amount of nickel sulfate to form the nickel-cobalt-based bimetallic oxide, and the addition amount of the platinum in the platinum salt and the nickel-cobalt bimetallic oxide nanocrystal/nitrogen-doped graphene binary compound is 1: 5.
application case Performance characterization
The platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst prepared by the method of example 3 is taken as an example for performance characterization.
1) X-ray powder diffraction Pattern (XRD)
Fig. 2 is an X-ray powder diffraction pattern, i.e., XRD pattern, of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst prepared by the method of example 3, from which characteristic peaks of platinum, graphene and manganese cobaltate can be clearly seen, which indicates that the composite product contains the three components. In addition, the XRD spectrum does not have the characteristic peak of graphite oxide, but only has one peak at about 25 degrees, indicating that graphite oxide has been reduced to graphene.
2) Microscopic analysis
Fig. 3A-B are field emission scanning electron microscope images of the platinum/manganese cobaltate nanocrystal/nitrogen doped graphene three-dimensional composite electrode catalyst, wherein fig. 3B is a partially enlarged view of fig. 3A. The composite electrode catalyst has an obvious highly-wrinkled three-dimensional self-supporting structure, the gaps among the graphene oxide nanosheets which are overlapped together are mutually communicated to form a microporous network, the sizes of the pores are distributed in the range of hundreds of nanometers to tens of micrometers, the pores have a large internal space, the platinum and manganese cobaltate nanocrystals are uniformly dispersed on the three-dimensional nitrogen-doped graphene network, and the platinum particles and the manganese cobaltate nanocrystals keep small particle sizes. When the mixture ratio of the present application is changed, a good three-dimensional porous network structure cannot be formed when the content of the nitrogen-doped graphene is too high (comparative example 3) or too low (comparative example 2). As shown in fig. 3C-D, when the content of graphene oxide is too high, sufficient space between sheets is not available to form a three-dimensional network structure, and a large amount of graphene is easily stacked and agglomerated to form a thicker carbon layer; when the content of the graphene oxide is too low, only sparse connection exists between the sheets, and the graphene component shows a typical two-dimensional shape and cannot form a three-dimensional network structure.
Fig. 4 is a transmission electron microscope image of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst. As can be seen, a plurality of particles with small particle size are uniformly dispersed on the ultrathin nitrogen-doped graphene nano sheet, and no obvious aggregation exists among the particles; the three-dimensional composite catalyst constructed by the interaction of the manganese cobaltate nanocrystal and the nitrogen-doped graphene is beneficial to more uniform distribution and smaller size of manganese cobaltate and platinum nanocrystal, effectively increases active sites, and well overcomes the problems of particle stacking and agglomeration.
The results show that the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst has an anti-stacking and anti-agglomeration three-dimensional porous network framework, and the components form good dispersion, large specific surface area and more active sites, so that the catalyst has higher catalytic performance and electrochemical activity.
3) Nitrogen adsorption and desorption test
As can be seen from the adsorption and desorption test graph of FIG. 5, the specific surface area of the catalyst is 240.4m2g-1The structure is rich in mesoporous structure.
4) Electrochemical methanol oxidation reaction test
The experimental method comprises the following steps: an electrocatalytic methanol oxidation test was performed on an electrochemical workstation (CHI760E, shanghai chenhua instruments ltd). A standard three-electrode system is adopted, and a Pt wire, a Saturated Calomel Electrode (SCE) and a glassy carbon electrode (GCE, 3mm) coated with a three-dimensional composite catalytic material are respectively used as a counter electrode, a reference electrode and a working electrode. The working electrode was prepared using a typical method: 2mg of the three-dimensional composite catalytic material was dissolved in a mixed solution (475. mu.l of water, 475. mu.l of ethanol and 50. mu.15% of Nafion), sonicated for 30min, and then 5. mu.1 of the above suspension was carefully dropped on the surface of the pretreated glassy carbon electrode (GCE, 3mm) and dried at room temperature. In the methanol oxidation performance test, the electrochemical active surface area (ECSA) and the methanol oxidation catalytic activity are measured by cyclic voltammetry, and the electrolyte is 0.5M H respectively2SO4Solution and 0.5M H2SO4And 1M CH3The scan rates of the OH mixed solution were all 50mV s-1. Meanwhile, the stability and methanol tolerance of the catalyst are evaluated by adopting a constant potential oxidation method and a chronopotentiometry method.
As can be seen from fig. 6A, the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst has the highest electrochemical active area, which indicates that the number of exposed active sites is the most; as can be seen from fig. 6B, the peak current of the forward cyclic voltammetry curve of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene composite electrode catalyst is the largest, which indicates that the catalytic activity of the catalyst is the best. Meanwhile, as shown in fig. 7, after a chronoamperometric test of 2000s, the catalyst still maintains a larger current, which indicates that the catalyst has excellent stability and antitoxic capability.
In addition, methanol oxidation activity was measured on the three-dimensional composite electrode catalysts prepared by the methods of examples 1 to 5 and comparative examples 1 to 4, and the results are shown in table 1.
TABLE 1 Performance index of catalysts prepared in examples 1 to 5 and comparative examples 1 to 4 for methanol oxidation reaction
Figure RE-GDA0002706642000000111
As can be seen from table 1, the catalysts prepared by the methods of examples 1 to 5 have higher electrochemical active area, higher methanol oxidation forward peak current, and higher catalytic activity than the composite electrode catalyst of the nickel-cobalt bimetallic oxide nanocrystal/nitrogen-doped graphene (comparative example 4) commonly used in the market. With the improvement of the contents of the nitrogen-doped graphene nanosheets and the platinum in the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene composite, the active surface area and the quality activity of the catalyst are increased, because the self-supporting effect of the nitrogen-doped graphene and the intercalation effect of the manganese cobaltate form a three-dimensional network skeleton structure with good dispersibility, the nanosheets are not stacked and agglomerated and tend to be uniformly dispersed, and further, the manganese cobaltate and platinum nanocrystal particles are more uniformly distributed and have smaller sizes, so that the catalytic activity of the composite electrode catalyst is improved; however, the addition amounts of the graphene sheet and the platinum are further increased, and in examples 4-5, the performance of the catalyst is reduced in comparison with that of example 3, and when the content of the nitrogen-doped graphene nanosheet is increased to the content of the comparative example 2, the performance of the catalyst is sharply reduced; this is because platinum particles aggregate to grow, thereby reducing active sites, while an excessively high content of graphene causes stacking and agglomeration of graphene sheets, thereby reducing catalytic activity. Accordingly, when the platinum content is decreased (comparative example 3), an effective amount of catalytic sites cannot be formed, and the catalytic activity is also decreased in response. Further analyzing the data of examples 1 to 5, it can be seen that when the content of manganese cobaltate is high (example 1), a large amount of manganese cobaltate may cause that graphene cannot form a good three-dimensional structure, and the conductivity of manganese cobaltate is poor, resulting in poor catalytic performance of the composite catalyst. Therefore, the proper addition proportion of the nitrogen-doped graphene, the manganese cobaltate and the platinum is beneficial to comprehensively exerting the catalytic performances of the nitrogen-doped graphene, the manganese cobaltate and the platinum, a synergistic effect is generated, and high catalytic activity and catalytic stability are further obtained. Through a large number of experiments, the proportion of each component is determined, and the methanol oxidation electrocatalyst with good catalytic performance can be obtained only under the content of the proportion.

Claims (10)

1. A preparation method of a platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst is characterized by comprising the following steps:
s1, preparing a graphene oxide dispersion liquid;
s2, adding cobalt salt, manganese salt and ammonia water into the graphene oxide dispersion liquid obtained in the step S1, uniformly stirring to prepare a manganese cobaltate/nitrogen-doped graphene precursor solution, wherein the addition amount of the graphene oxide and the manganese cobaltate is 1-20: 1-20, wherein the addition amount of nitrogen elements and graphene oxide in the ammonia water is 1: 1-100;
s3, carrying out hydrothermal reaction on the manganese cobaltate/nitrogen-doped graphene precursor solution obtained in the step S2 to obtain a hydrogel-like product, then dialyzing, washing with water, and freeze-drying to obtain three-dimensional manganese cobaltate nanocrystal/nitrogen-doped graphene;
s4, adding a platinum salt solution into the manganese cobaltate nanocrystal/nitrogen-doped graphene in the step S3, performing hydrothermal reaction, performing centrifugal washing, and performing freeze drying to obtain the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst, wherein the addition amount of the platinum in the platinum salt and the manganese cobaltate nanocrystal/nitrogen-doped graphene binary composite is 1: 1 to 20.
2. The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst as claimed in claim 1, wherein in step S2, the addition amount of the graphene oxide and the manganese cobaltate is 1-10: 1-10, wherein the addition amount of nitrogen elements in the ammonia water and the addition amount of graphene oxide are 1: 20.
3. the preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst as claimed in claim 2, wherein in step S2, the addition amount of the graphene oxide and the manganese cobaltate is 1: 2, the mass ratio of the mass of the nitrogen element in the ammonia water to the addition amount of the graphene oxide is 1: 20.
4. the preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst as claimed in claim 1, wherein in step S4, the addition amount of the platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene binary composite in the platinum salt is 1: 3 to 10.
5. The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst as claimed in claim 4, wherein in step S4, the addition amount of the platinum and manganese cobaltate nanocrystal/nitrogen-doped graphene binary composite in the platinum salt is 1: 5.
6. the preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst according to claim 1, wherein in step S2, the cobalt salt is cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt acetate or cobalt chloride; the manganese salt is manganese nitrate, manganese acetate, manganese sulfate, manganese acetate or manganese chloride.
7. The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen doped graphene three-dimensional composite electrode catalyst as claimed in claim 1, wherein in step S1, the concentration of the graphene oxide dispersion liquid is 0.1-5 g/L.
8. The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst according to claim 1, wherein in step S2, the stirring conditions are as follows: magnetic stirring is carried out for 1 to 24 hours at the temperature of between 0 and 100 ℃.
9. The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen-doped graphene three-dimensional composite electrode catalyst according to claim 1, wherein in step S3, the hydrothermal reaction conditions are as follows: the reaction time is 2-48h at 100-200 ℃, the dialysis water washing time is 1-10 times, and the drying pressure during freeze drying is 10-200 Pa.
10. The preparation method of the platinum/manganese cobaltate nanocrystal/nitrogen doped graphene three-dimensional composite electrode catalyst according to claim 1, wherein in the step S4, the hydrothermal reaction conditions are as follows: the reaction time is 2-48h at 100-200 ℃, the centrifugal water washing time is 1-10 times, and the drying pressure during freeze drying is 10-200 Pa.
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