Electrodeposition of Cobalt in a Pyrrolidinium-Based Ionic Liquid Under a Magnetic Field

Abstract

Cobalt (Co) is well-known as a hard-magnetic material for its tailorable magnetic properties. Nowadays, a pyrrolidinium-based ionic liquid, composed of 1-butyl-1-methylpyrrolidinium (BMP+) and bis(trifluromethylsulfonyl)amide (TFSA–), has drawn more attention for the electrodeposition of various transition metals because of its wide electrochemical potential window, acceptable ionic conductivity, and high stability against moisture. Although the redox reaction of Co species has been reported in BMPTFSA, the electrochemical behavior of Co species under a magnetic field has not been explored in this ionic liquid.1-3 In this study, the electrodeposition of Co has been performed in BMPTFSA under a static magnetic field. Co(TFSA)2 was prepared by the reaction of CoCO3 with HTFSA. A Teflon made, double compartment cell was used for the electrochemical measurements using a glassy carbon (GC) as a working electrode, a platinum mesh as a counter electrode, and a silver wire immersed in BMPTFSA containing 0.1 M AgCF3SO3 as a reference electrode. A neodymium magnet (NdFeB) was attached to the back of the GC electrode. The diameter of the magnet was 6 mm and the magnetic flux density was 530 mT. Potentiostatic cathodic reduction applying –1.6 and –2.0 V was conducted under the magnetic field in BMPTFSA containing Co(TFSA)2 at 25 °C. Nanowire-shaped deposits were obtained on the GC electrode after the electrodeposition at both potentials. The presence of Co in the deposits was confirmed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. However, no diffraction peak was observed in the deposits by X-ray diffraction. The deposits were further examined by transmission electron microscopy. The lattice fringe corresponding to (111) plane of Co was found in the deposits, indicating the deposits were composed of metallic Co nanoparticles.References(1) R. Fukui, Y. Katayama, and T. Miura, Electrochemistry, 73, 567 (2005).(2) Y. Katayama, R. Fukui, and T. Miura, J. Electrochem. Soc., 154, D534 (2007).(3) Y. Katayama, R. Fukui, and T. Miura, Electrochemistry, 81, 532 (2013).