Electrochemical Behavior of Cobalt and Samarium Species in an Amide-Type Ionic Liquid

Abstract

Rare earth-transition metal alloys/nanoparticles (NPs) have drawn intensive significance in a wide range of applications in automobiles, data storage, magnetoelectronic, electromechanical, and electronic devices due to their excellent magneto-crystalline anisotropy. Among them, cobalt (Co)-samarium (Sm) alloys are of great interest. Although there are many reports on the preparation of Co-Sm alloys in different media by different techniques, the electrodeposition of Co-Sm alloys/NPs has not been confirmed in an aprotic ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), which has high cathodic stability. In the present study, the electrochemical behavior of Co and Sm species was investigated in BMPTFSA at different temperatures. Co(TFSA)2 and Sm(TFSA)3 were prepared by the reactions of CoCO3 and Sm2O3 with HTFSA, respectively, and dissolved in BMPTFSA 1-3. Electrochemical measurements were conducted with an air-tight cell using glassy carbon (GC) as a working electrode, a Co wire as a counter electrode, and an Ag wire immersed in 0.1 M AgCF3SO3/BMPTFSA as a reference electrode. Potentiostatic cathodic reduction at –2.5 V on a GC electrode was conducted in BMPTFSA containing 30 mM Co(TFSA)2 and 5 mM Sm(TFSA)3 at 25 and 100 oC. The lower concentration of Sm(III) was preferred than that of Co(II) because of the difference in the diffusion coefficients of Co(II) and Sm(III) ions in BMPTFSA. Deposits on the GC electrode surface were found after electrodeposition. The presence of Co and Sm in the deposits was confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The deposits were found to be amorphous by X-ray diffraction. In addition, the electrolyte after electrolysis was examined by transmission electron microscopy (TEM). The formation of the NPs with lattice fringes was confirmed by TEM. The spots observed in the electron diffraction image of the NPs could be assigned to (111) and (110) planes of SmCo7. EDX confirmed the presence of Co and Sm in the NPs. Therefore, SmCo7 NPs were considered to be prepared in this ionic liquid.