Electrochemical Synthesis of Co-Nd Films in Urea and Choline Chloride Deep Eutectic Solvents
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DUCTION
RARE earth elements, with excellent optical and electromagnetic properties, have been widely used in the metallurgical, glass ceramics, petrochemical, agriculture, and aerospace fields. Molten salt electrolysis in REF3-LiF-RE2O3-based electrolytes at 1273 K to 1373 K is the main process for the production of rare earth metals and their alloys. The high electrolysis temperature leads to oxidation of carbon anodes and volatile loss of fluoride electrolytes. In addition, the current efficiency and electrical energy efficiency are less than 70 and 25 pct, respectively. If rare earth metals and their alloys can be prepared by electrodeposition at room temperature, the electrical energy efficiency can be increased to more than 80 pct and the production costs and pollutant emissions could be reduced.
AIMIN LIU is with the Key Laboratory for Ecological Metallurgy of Multimetallic Mineral (Ministry of Education), Northeastern University, Shenyang 110819, P.R. China. ZHONGNING SHI is with the State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, P.R. China. Contact email: [email protected] RAMANA G. REDDY is with the Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487. Contact email: [email protected] Manuscript submitted November 6, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
The rare earth metals can react with water and acid, and the standard electrode potentials of rare earth metals are so negative that their electrochemical deposition in aqueous solution is affected by hydrogen ion discharge. The deposition potential of rare earth metals in nonaqueous medium positively shifted, and the influence of hydrogen ion discharge can be avoided, so that the rare earth metals can be electrodeposited in nonaqueous electrolytes such as room temperature ionic liquids. Bhatt et al.[1] found that a series of [R4X]N(SO2CF3)2 (X = N, P, As) ionic liquids with a wide electrochemical window (larger than 5.6 V) were suitable for electrodeposition of La, Sm, and Eu. Rao et al.[2] prepared Eu metal in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPNTf2) ionic liquids and found that the electrochemical reduction of Eu(III) ions is a two-step electrode reaction. Legeai et al.[3] found that the electrochemical window of 1-octyl-1-methylpyrrole bistrifluoromethanesulfonimide salt (OMPTf2N) ionic liquids is 4.8 V, and a La film with thickness of 350 nm was obtained by potentiostatic electrodeposition for 2 hours. Hatchett et al.[4] used Ce2(CO3)3 as a raw material to electrodeposit micron-sized Ce particles in trimethyl-n-butylammonium bis(trifluoromethanesulfonyl)imide ([Me3NBu][TFSI]) ionic liquids. Matsumiya and co-workers[5,6] reported the electrodeposition of Pr, Nd, and Dy in triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide ([P2225][TFSA]) ionic liquids. However, the preparation of the aforementioned ionic liquids is
complicated and costly, and the rare earth raw materials are complex organic salts, such as La((NSO
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