Molten salt electrochemical preparation method of carbon-coated low-melting-point metal nano material
Technical Field
The invention belongs to the technical field of material metallurgy, and particularly relates to a molten salt electrochemical preparation method of a carbon-coated low-melting-point metal nano material.
Background
Metals such as Sn, Bi, Sb, Pb, In, Ga, etc. have low melting points, so the nanostructures of these simple metals are physically unstable, and these metals have a high tendency to oxidize when exposed to air, particularly Sn, Bi, Pb, In, Ga. The carbon-coated low-melting-point metal powder material has the advantages of excellent electronic conductivity, high chemical stability, capability of preventing metal nanoparticles from agglomerating and the like, and is widely applied to the fields of electrocatalysis, batteries, capacitors and the like.
Currently, carbon-coated low-melting-point metal materials are generally prepared by an electrospinning method, a ball milling method, a hydrothermal-carbothermic method and the like. For example, Energy Storage mater, 18(2019) 229-; the patent CN 110400921A adopts a ball milling mode to prepare a carbon-coated metal material; the preparation of carbon-coated metal materials by hydrothermal method and carbonization of precursors is also widely used (Nano Lett.2020,20,4464-4471, J.electrochem.Soc., 152-7) A1452-A1457 (2005); CN 201810055854.8). In all the above methods, organic substances (such as sucrose, glucose, polyacrylonitrile, dimethylformamide, dopamine, etc.) are used as carbon sources, and certain compounds of low-melting point metals are used as metal sources, and the organic substances are prepared first, and then the target structure product is obtained through further carbonization reaction. The regulation and control difficulty is high, the operation steps are complex, and the carbonization temperature is high. .
Disclosure of Invention
The invention aims to provide a molten salt electrochemical preparation method of a carbon-coated low-melting-point metal nano material, which has the advantages of simple steps, mild reaction conditions and controllable product morphology and structure (such as adjustment through parameters of reaction time, temperature, electrolytic current and the like). In particular, the method adopts greenhouse gas carbon dioxide as a carbon coating raw material, does not need organic matters as a carbon source, and can avoid the difficulty in controlling the process when the organic matters are violently pyrolyzed and the additional process required by preparing the organic matters in the prior art. The implementation of the method can realize the modification and value-added of the low-melting-point metal and can realize the emission reduction and value-added conversion of greenhouse gas carbon dioxide.
In order to achieve the purpose, the technical scheme is as follows:
the molten salt electrochemical preparation method of the carbon-coated low-melting-point metal nano material comprises the following steps:
the method comprises the steps of taking carbonate molten salt as electrolyte, taking low-melting-point metal as an electrode in an inert atmosphere containing carbon dioxide, applying oxidation current to the low-melting-point metal, then applying reduction current to the low-melting-point metal, and washing and drying the low-melting-point metal to obtain the powder of the carbon-coated low-melting-point metal sphere core.
According to the scheme, the carbonate is Li2CO3、Na2CO3、K2CO3One or a mixture thereof.
According to the scheme, the inert atmosphere is argon, nitrogen or helium, wherein the volume fraction of carbon dioxide is 0.001-99.99%.
According to the scheme, the electrochemical preparation of the molten salt adopts two electrodes, wherein one electrode is the low-melting-point metal, and the other electrode is graphite, metal, alloy or SnO2Perovskite ceramics, platinum or gold.
According to the scheme, the low-melting-point metal is one or more of Sn, Bi, Sb, Pb, In and Ga.
According to the scheme, the oxidation current is 0.001-5A cm-2。
According to the scheme, the reduction current is 0.001-5A cm-2。
According to the scheme, the time for oxidation or reduction is 1 s-12 h.
According to the scheme, the process of oxidation and reduction is circulated for 1-100 times.
According to the scheme, the method further comprises the following pretreatment steps:
uniformly mixing the carbonates, putting the mixture into a crucible, heating the mixture to 100-300 ℃, and keeping the temperature for 12-48 h to remove water;
then at 5-10 ℃ for min-1Heating to 450-800 ℃ and then carrying out electrolysis.
According to the scheme, the washing process is respectively washed for three times by deionized water and ethanol.
Compared with the prior art, the invention has the beneficial effects that:
the method takes low-melting-point metal (Sn, Bi, Sb, Pb, In and Ga) as an electrode, and carries out electrolysis In a carbonate molten salt In a mode of oxidation and reduction to obtain a carbon-coated low-melting-point metal nano material on the surface of the low-melting-point metal electrode; the formation of a product coating structure and the relative content of metal and carbon are effectively controlled by controlling the reaction time, the temperature and the electrolytic current.
According to the invention, carbon dioxide is used as a carbon source by adopting a molten salt electrolysis method, and is directionally converted into the core-shell structure material of the carbon-coated low-melting-point metal on the liquid metal electrode, so that the modification and value-added of the low-melting-point metal can be realized, and the emission reduction and value-added conversion of greenhouse gas carbon dioxide can be realized.
Drawings
FIG. 1: XRD pattern of carbon-coated Sn nanomaterial obtained in example 1;
FIG. 2: electron micrograph of carbon-coated Sn nanomaterial obtained in example 1.
Detailed Description
The following examples further illustrate the technical solutions of the present invention, but should not be construed as limiting the scope of the present invention.
Example 1:
electrochemical treatment with graphite and low melting point Sn as electrodes, Li2CO3The molten salt is an electrolyte. Firstly at 5 ℃ for min-1Heating to 250 deg.C and maintaining for 24 hr to make Li2CO3The water in the molten salt is completely volatilized. Then at 5 deg.C for min-1Heating to 800 deg.C, introducing argon gas containing carbon dioxide 0.001 vt% as protective atmosphere, maintaining the temperature at 800 deg.C when molten salt is completely melted, and applying 1000mA cm to liquid Sn electrode-2Oxidizing for 1800s, and applying 1000mA cm-2And (4) reducing for 4800 s. And after the electrolysis is finished, taking out the Sn electrode, and respectively washing the Sn electrode for three times by using deionized water and absolute ethyl alcohol to obtain the carbon-coated Sn nano material with the spherical structure.
The XRD of the carbon-coated Sn nano material obtained in the embodiment is shown in figure 1, and the XRD pattern shows that the components in the nano material collected by the cathode are carbon and Sn; an electron microscope (TEM) of the carbon-coated Sn nanomaterial obtained in this example is shown in fig. 2, and the TEM indicates that the morphology of the obtained cathode product is characterized by Sn @ C spheres with a core-shell structure in which metal Sn is used as a core and carbon is used as a shell.
Example 2:
electrochemical treatment with graphite and low melting point Sn as electrodes, Li2CO3-Na2CO3-K2CO3The molten salt is an electrolyte. Firstly at 5 ℃ for min-1Heating to 250 deg.C and maintaining for 24 hr to make Li2CO3-Na2CO3-K2CO3The water in the molten salt is completely volatilized. Then at 5 deg.C for min-1Heating to 500 deg.C, introducing argon gas as protective atmosphere, heating to 700 deg.C when molten salt is completely melted, introducing carbon dioxide gas (high purity carbon dioxide gas), and applying 2Acm to liquid Sn electrode-2Oxidizing for 3000s, and applying 5Acm-2Reducing for 3000s, and circulating 100 times in this way. And after the electrolysis is finished, taking out the Sn electrode, and respectively washing the Sn electrode for three times by using deionized water and absolute ethyl alcohol to obtain the carbon-coated tin nano material with the spherical structure.
Example 3:
using graphite and low-melting point bismuth as electrodes, Li2CO3-Na2CO3The molten salt is an electrolyte. Firstly at 5 ℃ for min-1Heating to 300 deg.C and maintaining for 24 hr to make Li2CO3-Na2CO3The water in the molten salt is completely volatilized. Then at 5 deg.C for min-1Heating to 800 ℃, introducing nitrogen containing 90 vol% of carbon dioxide as protective atmosphere, and applying oxidation current of 200mAcm to the liquid bismuth when the molten salt is completely melted-2Oxidizing for 1h, and applying reducing current of 500mAcm-2The reduction time is 2h, and the circulation is carried out for 2 times. And after the electrolysis is finished, taking out the cathode, and respectively washing the cathode for three times by using deionized water and absolute ethyl alcohol to obtain the carbon-coated bismuth nano material.
Example 4:
in SnO2And low melting point indium as an electrode, Li2CO3-Na2CO3-K2CO3The molten salt is an electrolyte. Firstly at 5 ℃ for min-1Heating to 300 deg.C and maintaining for 24 hr to make Li2CO3-Na2CO3-K2CO3In molten saltThe water content is completely volatilized. Then at 5 deg.C for min-1Heating to 450 ℃, introducing helium containing 1 vol% of carbon dioxide as protective atmosphere, and applying oxidation current of 1mAcm to liquid indium when molten salt is completely melted-2Oxidizing for 100s, and applying reduction current of 10mAcm-2Reducing for 300s, and circulating 30 times in this way. And after the electrolysis is finished, taking out the cathode, and respectively washing the cathode for three times by using deionized water and absolute ethyl alcohol to obtain the carbon-coated indium nano material.
Example 5:
using graphite and low melting point lead as electrodes, Li2CO3-Na2CO3Molten salt as electrolyte, and heating at 5 deg.C for min-1Heating to 300 deg.C and maintaining for 24 hr to make Li2CO3-Na2CO3The water in the molten salt is completely volatilized. Then at 5 deg.C for min-1Heating to 800 ℃, introducing nitrogen containing 90 vol% of carbon dioxide as protective atmosphere, and applying oxidation current of 2A cm to the liquid lead when the molten salt is completely melted-2Oxidizing for 1000s, and applying a reducing current of 2Acm-2The reduction time is 3000s, and the cycle is 4 times. And after the electrolysis is finished, taking out the cathode, and respectively washing the cathode for three times by using deionized water and absolute ethyl alcohol to obtain the carbon-coated lead nano material.