ИСТИНА

Rare-earth elements (REEs) are one of the most important raw materials and are of great importance for the modern high-tech industry. Low-temperature electrochemical deposition of REE-containing materials for the purpose of recycling and obtaining functional materials can provide a real alternative to the currently used high-temperature processes of molten salt electrolysis. The growing interest in ionic liquids (ILs) as media for electrochemical deposition of metals and semiconductors is due to their excellent physicochemical properties, including non-volatility, intrinsic conductivity, thermal and electrochemical stability. The possibility of electrodeposition from IL-based solutions was demonstrated for various metals and semiconductors from the first to sixteenth groups of the periodic table. However, studies on electrodeposition of REEs from ILs are scarce. Here, we present the investigation of electrochemical deposition of some chosen REEs in the 1-butyl-1-methylpyrrolidinium dicyanamide IL ([BMP][DCA]) at room temperature. Analysis of literature data shows that the dicyanamide ILs can be a proper choice as a medium for lanthanide deposition due to their relatively low viscosity (for [BMP][DCA], 50 mPa s at 293 K) and good solubilizing ability. The electrodeposition of REEs is studied on different single crystal electrodes with a controlled surface structure (Pt(111), Au(111), HOPG) as well as on a polished glassy carbon electrode. Cyclic voltammetry and chronoamperometry in the absence and presence of REE ions are used to identify REE-related electrochemical processes, while atomic force microscopy (AFM) is employed to characterize the deposit morphology obtained after potentiostatic polarization of the working electrodes. The voltammetric results demonstrate clear reduction of REEs at potentials more positive than reductive degradation of the IL. The AFM data confirm the REE deposition and reveal a strong dependence of deposit morphology on the substrate material and electrode potential, at which the deposit is formed. We also use the obtained data as a basis for studies on electrochemical deposition of REE–transition metal (TM) alloys from the dicyanamide ILs. As demonstrated in literature, TM with a more positive reduction potential can induce REE co-deposition with its reduction onset shifted to less negative potentials.