CN109811368B - Lithium ion reinforced inert anode for molten salt electrolysis system and preparation method thereof - Google Patents
Lithium ion reinforced inert anode for molten salt electrolysis system and preparation method thereof Download PDFInfo
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- CN109811368B CN109811368B CN201910212158.8A CN201910212158A CN109811368B CN 109811368 B CN109811368 B CN 109811368B CN 201910212158 A CN201910212158 A CN 201910212158A CN 109811368 B CN109811368 B CN 109811368B
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Abstract
The invention relates to a lithium ion reinforced inert anode for a molten salt electrolysis system and a preparation method thereof. The inert anode comprises a metal matrix of iron, nickel, titanium and the like, and a lithium ion reinforced metal oxide film layer attached to the surface of the metal matrix, wherein the film layer is of a single-layer structure or a multi-layer structure, and the outermost layer of the film layer is a solid solution or compound formed by combining metal oxide and lithium oxide. The inert anode has the advantages that due to the unique structure and the outer layer components, fluorine and chlorine ions can be effectively prevented from permeating into the metal matrix, and corrosion to the metal matrix is avoided, so that the electrode is long in service life and low in use cost, has excellent corrosion resistance, electronic conductivity and oxygen evolution catalytic activity, can stably evolve oxygen when being used in a molten salt electrolysis system, and the application range of the molten salt electrolysis system is expanded.
Description
Technical Field
The invention relates to the technical field of metallurgy, in particular to a lithium ion reinforced inert anode for a molten salt electrolysis system and a preparation method thereof.
Background
Although the reserve of aluminum in the crust is higher than that of iron, the price of aluminum metal is much higher than that of iron metal, mainly because the smelting process cost of aluminum is too high. At present, the Hall-Heroult method is generally adopted in industry, fluoride fused salt is taken as electrolyte to prepare metal aluminum by electrolysis, and a consumable carbon anode is taken as a key factor of higher cost. Firstly, the method consumes a large amount of high-quality carbon materials in the smelting process, and the material cost accounts for 14-22% of the aluminum production cost; secondly, the consumable anode needs to be replaced regularly, which increases the labor cost and reduces the production efficiency; furthermore, the conductivity of the consumable carbon anode is not ideal enough, and the inter-polar distance is too large, so that the energy efficiency of aluminum electrolysis is only highAbout 40%, which increases the energy consumption cost. In addition, the use of consumable carbon anodes also releases large amounts of CO2And a small amount of toxic gas, causing serious environmental problems. Therefore, the development of a novel inert anode for replacing the existing consumable carbon anode in the aluminum electrolysis system has great economic and environmental benefits.
The chloride electrolysis process has great application prospect in the field of metal smelting, and can greatly simplify the smelting process of titanium metal and obviously reduce the smelting cost of the titanium metal on one hand; on the other hand, nanowires and nanoparticles of silicon and germanium can be prepared, so that an excellent lithium ion battery cathode material is obtained; can also be used for preparing high-melting-point metals such as tungsten, molybdenum, tantalum, hafnium, zirconium, niobium and the like and carbides thereof. The chloride electrolysis process is also an ideal separation and recovery method of spent fuel in nuclear power industry. An important factor for the lack of large-scale industrial application of chloride electrolysis processes is the lack of suitable inert anodes, so that stable oxygen evolution of the inert anodes is critical to the success of the chloride electrolysis process.
In the fluoride and chloride electrolysis process, the anode working environment has the characteristics of strong corrosivity, high temperature, oxygen enrichment, positive polarization potential and the like, and great challenge is formed on the selection of an inert anode material. The inert anode materials which are researched more at present comprise ceramics, metals and the like, such as Chinese patents CN102206837A, CN101935852A, CN102560562A and CN 102586853A. These inert anode materials are limited by their respective defects, for example, ceramic inert anodes have problems of poor conductivity, poor thermal shock resistance, inconvenient connection and the like, and cermet inert anodes have problems of selective dissolution of metal phases and the like, and are difficult to put into industrial application.
It is known that a layer of metal oxide film is generated on the surface of a metal material by a pre-oxidation method, so that the corrosion resistance of a metal inert anode can be effectively improved, but fluorine ions or chlorine ions still permeate into the oxide film in the anode polarization process and react with a metal matrix to generate metal fluoride or chloride, so that the anode is corroded to damage the oxide film, and the protection effect of the oxide film is lost to cause the failure of the pre-oxidized metal inert anode.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a lithium ion reinforced inert anode for a molten salt electrolysis system. Experiments show that the lithium oxide component dissolved or combined in the oxide film layer on the surface of the metal matrix can effectively prevent fluorine ions and chlorine ions from permeating and eroding the metal matrix, so that the lithium oxide component can stably exist in fluoride molten salt and chloride molten salt and keep good performance, becomes an excellent oxygen evolution inert anode and can be used for preparing aluminum by electrolysis. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the lithium ion reinforced inert anode for the molten salt electrolysis system comprises a metal matrix and a lithium ion reinforced metal oxide film layer coated on the surface of the metal matrix; the lithium ion reinforced metal oxide film layer is composed of at least one of lithiated chromium oxide, nickel oxide, cobalt oxide and manganese oxide, wherein the lithium content is 0.1-14 wt%.
Further, the metal matrix is specifically any one or an alloy of several of iron, nickel, titanium, cobalt, copper, manganese, aluminum, magnesium, zirconium and chromium.
Further, an unlithiated metal oxide transition layer is also included between the lithium ion enhanced metal oxide film layer and the metal substrate. The metal oxide transition layer comprises one or more of chromium oxide, nickel oxide, titanium oxide, iron oxide, cobalt oxide, manganese oxide and aluminum oxide.
Furthermore, a metal and metal oxide cross-distribution layer is also arranged between the lithium ion reinforced metal oxide film layer and the metal substrate.
Furthermore, the thickness of the film layer coated on the surface of the metal substrate is 1-1000 μm.
Further, the molten salt used in the electrolysis of the lithium ion reinforced inert anode is a fluoride salt, a chloride salt or a mixture thereof with the mass fraction of more than 60%.
The preparation method of the lithium ion enhanced inert anode for the molten salt electrolysis system comprises the following steps: forming a specific protective layer on the surface of the metal matrix by any one or more methods of spraying, vapor deposition, chemical oxidation and electrochemical oxidation.
Compared with the prior art, the invention has the following beneficial effects: (1) the outermost layer of the inert anode is a solid solution or compound formed by combining metal oxides such as chromium oxide and the like and lithium oxide, and lithium ions fill gaps of the metal oxides, so that fluorine and chlorine ions can be effectively prevented from permeating into the metal matrix to corrode the metal matrix, the service life of the electrode is longer, and the use cost is lower; (2) the inert anode has excellent corrosion resistance, electronic conductivity and oxygen evolution catalytic activity, can stably evolve oxygen when used in an electrolytic aluminum molten salt system, expands the application range of the molten salt electrolytic system and is beneficial to reducing the price of an electrolytic aluminum product; (3) the thickness and the number of layers of the protective layer coated on the surface of the metal matrix are flexible and controllable, and the preparation mode of the protective layer has more selectivity.
Drawings
FIG. 1 is a schematic structural diagram of a lithium ion enhanced inert anode according to the present invention;
FIG. 2 is a photograph of a cross section of a lithium ion-enhanced inert anode prepared in example 2 of the present invention.
Wherein 1 represents a metal matrix, and 2 represents a lithium ion-strengthening metal oxide film.
Detailed Description
In order to make those skilled in the art fully understand the technical solutions and advantages of the present invention, the following embodiments are further described.
Example 1
The method comprises the steps of taking 310S stainless steel as a substrate, taking chromium oxide and lithium oxide (the mass ratio of the chromium oxide to the lithium oxide is 83.6: 16.4) as coating raw materials, and preparing a layer of LiCrO with the thickness of 10 microns on the surface of the stainless steel substrate by adopting a plasma spraying method2(Cr2O3·Li2O) an oxide film layer to obtain the lithium ion enhanced chromium oxide inert anode taking stainless steel as a matrix.
At 750 ℃, with CaCl2NaCl-CaO molten salt (molar ratio CaCl)2NaCl, CaO 48:48: 4%) as an electrolyte, and TiO2The cathode was prepared and the service behavior of the lithium ion enhanced chromium oxide inert anode was tested by means of 2.9V constant cell pressure electrolysis. The results show that the inert anode is in CaCl2After the system works for 1000 hours in a NaCl-CaO system, the stable oxygen evolution can be still maintained.
Example 2
Using metal nickel as base body, adopting air preoxidation method to produce a layer of nickel oxide on its surface, then using lithium oxide as raw material, using ion beam energy of 200keV and adopting ion implantation method to prepare a layer of lithiated nickel oxide (Li) with thickness of 12 micrometers on the nickel oxide surface0.15Ni1.05O2) And (3) layering to obtain the lithium ion enhanced nickel oxide inert anode taking metallic nickel as a matrix.
The inert anode has a structure shown in fig. 1, and a cross-sectional optical photograph thereof is shown in fig. 2. As can be seen from the figure, the outer layer was a dense lithiated nickel oxide layer of 12 μm thickness, and a 30 μm thick metal oxide-metal cross-distribution layer was present between the lithiated nickel oxide layer and the metal substrate.
At 650 deg.C, using LiCl-Li2O molten salt (molar ratio LiCl: Li)2O-98: 2) was used as the electrolyte, and spent fuel oxide was used as the cathode, and the service behavior of the above lithium ion-enhanced nickel oxide inert anode was tested by means of 2.9V constant cell pressure electrolysis. The results show that the inert anode is on LiCl-Li2After the O system works for 200 hours, the stable oxygen evolution can be still maintained.
Example 3
Taking nickel-cobalt alloy as a substrate, preparing a layer of LiCoO with the thickness of 30 mu m on the surface of the nickel-cobalt alloy by adopting an electrochemical pre-oxidation method2(Co2O3·Li2O) to obtain the lithium ion enhanced cobalt oxide inert anode taking the nickel-cobalt alloy as a matrix.
At 850 ℃ with CaCl2CaO molten salt (molar ratio CaCl)2CaO 98:2) as electrolyte, CaWO4Making cathode at 200mA/cm2The service behavior of the lithium ion enhanced cobalt oxide inert anode is tested by adopting a constant current electrolysis mode under the condition of anode current density. The results show that the inert anode is in CaCl2-CaO bodyAfter the system is operated for 100 hours, the stable oxygen evolution can be still maintained.
Example 4
Preparing a layer of LiMnO with the thickness of 40 mu m on the surface of an alloy matrix by taking a nickel-based alloy as a matrix and taking manganese oxide and lithium oxide (the mass ratio of manganese oxide to lithium oxide is 84.06: 15.94) as raw materials and adopting a physical vapor deposition method2And obtaining the lithium ion enhanced manganese oxide inert anode taking the nickel-based alloy as the matrix.
At 900 deg.C, with LiF-Li2CO3Molten salt (molar ratio LiF: Li)2CO396:1) as electrolyte, and nickel sheet as counter electrode at 200mA/cm2The service behavior of the lithium ion enhanced manganese oxide inert anode is tested by adopting a constant current electrolysis mode under the condition of the anode current density. The results show that the inert anode is in LiF-Li2CO3After the system works for 600 hours, the stable oxygen evolution can be still maintained.
Example 5
A316L stainless steel is taken as a substrate, cobalt oxide is taken as a raw material, a cobalt oxide layer with the thickness of 10 mu m is firstly prepared on the surface of the stainless steel substrate by adopting a spraying method, then cobalt oxide and lithium oxide (the mass ratio of the cobalt oxide to the lithium oxide is 84.7: 15.3) are taken as raw materials, and a LiCo O layer with the thickness of 10 mu m is prepared on the surface of the cobalt oxide layer2(Co2O3·Li2O) to obtain the cobalt oxide-lithium ion reinforced cobalt oxide composite oxide layer inert anode taking 316L stainless steel as a matrix.
At 850 ℃, NaF-AlF3-NaCl-CaF2-Al2O3Molten salt (mass ratio NaF: AlF)3:NaCl:Ca F2:Al2O344:40:8:5:3) as electrolyte, graphite as counter electrode at 400mA/cm2The service behavior of the cobalt oxide-lithium ion enhanced cobalt oxide composite oxide layer inert anode is tested by adopting a constant current electrolysis mode under the condition of anode current density. The results show that the inert anode is in NaF-AlF3-NaCl-CaF2-Al2O3After the system works for 2000 hours, the stable oxygen evolution can be still maintained.
Example 6
A layer of Li CrO with the thickness of 10 mu m is prepared on the surface of an alloy matrix by using a zirconium alloy as the matrix and using chromium oxide and lithium oxide (the mass ratio of the chromium oxide to the lithium oxide is 83.6: 16.4) as raw materials and adopting a chemical vapor deposition method2(Cr2O3·Li2O) an oxide film layer to obtain the lithium ion enhanced chromium oxide inert anode taking zirconium alloy as a matrix.
At 960 deg.C, cryolite-alumina fused salt is used as electrolyte, graphite is used as counter electrode, and the concentration of the electrolyte is 400mA/cm2The service behavior of the lithium ion enhanced chromium oxide inert anode is tested by adopting a constant current electrolysis mode under the condition of the anode current density. The result shows that the inert anode can still keep stable oxygen evolution after working for 800 hours in a cryolite-alumina molten salt system.
Claims (8)
1. A lithium ion reinforced inert anode for a molten salt electrolysis system is characterized by comprising a metal matrix and a lithium ion reinforced metal oxide film layer coated on the surface of the metal matrix; the lithium ion-reinforced metal oxide film layer is composed of at least one of lithiated chromium oxide, lithiated nickel oxide, lithiated cobalt oxide and lithiated manganese oxide; and a metal and metal oxide cross-distribution layer is also arranged between the lithium ion reinforced metal oxide film layer and the metal matrix.
2. The inert anode of claim 1, wherein: the content of lithium in the lithium ion reinforced metal oxide film layer is 0.1 wt% -14 wt%.
3. The inert anode of claim 1, wherein: the metal matrix is specifically any one or an alloy of several of iron, nickel, titanium, cobalt, copper, manganese, aluminum, magnesium, zirconium and chromium.
4. The inert anode of claim 1, wherein: and an unlithiated metal oxide transition layer is also arranged between the lithium ion reinforced metal oxide film layer and the metal matrix.
5. The inert anode of claim 4, wherein: the metal oxide transition layer comprises one or more of chromium oxide, nickel oxide, titanium oxide, iron oxide, cobalt oxide, manganese oxide and aluminum oxide.
6. The inert anode of claim 1, wherein: the thickness of the film layer coated on the surface of the metal substrate is 1-1000 μm.
7. The inert anode of claim 1, wherein: the molten salt used in the electrolysis of the lithium ion enhanced inert anode is fluoride salt, chloride salt or a mixture thereof with the mass fraction of more than 60%.
8. The method of any of claims 1-7 for the preparation of a lithium ion enhanced inert anode for a molten salt electrolysis system, characterized by the steps of: forming a specific protective layer on the surface of the metal matrix by any one or more methods of spraying, vapor deposition, chemical oxidation and electrochemical oxidation.
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| EP0306100A1 (en) * | 1987-09-02 | 1989-03-08 | MOLTECH Invent S.A. | A composite ceramic/metal material |
| WO1990010735A1 (en) * | 1989-03-07 | 1990-09-20 | Moltech Invent S.A. | An anode substrate coated with rare earth oxycompounds |
| WO2004018082A1 (en) * | 2002-08-21 | 2004-03-04 | Pel Technologies Llc | Cast cermet anode for metal oxide electrolytic reduction |
| EP1546436A1 (en) * | 2002-08-20 | 2005-06-29 | MOLTECH Invent S.A. | Protection of metal-based substrates with hematite-containing coatings |
| CN107740143A (en) * | 2017-09-29 | 2018-02-27 | 武汉大学 | A kind of iron-based inert anode with ferrous acid lithium diaphragm and preparation method thereof, application |
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| US6821312B2 (en) * | 1997-06-26 | 2004-11-23 | Alcoa Inc. | Cermet inert anode materials and method of making same |
| US7033469B2 (en) * | 2002-11-08 | 2006-04-25 | Alcoa Inc. | Stable inert anodes including an oxide of nickel, iron and aluminum |
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Patent Citations (7)
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| EP0306100A1 (en) * | 1987-09-02 | 1989-03-08 | MOLTECH Invent S.A. | A composite ceramic/metal material |
| WO1989001992A1 (en) * | 1987-09-02 | 1989-03-09 | Moltech Invent S.A. | A composite ceramic/metal material |
| WO1990010735A1 (en) * | 1989-03-07 | 1990-09-20 | Moltech Invent S.A. | An anode substrate coated with rare earth oxycompounds |
| EP1546436A1 (en) * | 2002-08-20 | 2005-06-29 | MOLTECH Invent S.A. | Protection of metal-based substrates with hematite-containing coatings |
| US20060003084A1 (en) * | 2002-08-20 | 2006-01-05 | Nguyen Thinh T | Protection of metal-based substrates with hematite-containing coatings |
| WO2004018082A1 (en) * | 2002-08-21 | 2004-03-04 | Pel Technologies Llc | Cast cermet anode for metal oxide electrolytic reduction |
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