Investigation of electrodeposition behavior for Nd(III) in [P2225][TFSA] ionic liquid by EQCM methods with elevated temperatures

Abstract

The electrodeposition behavior of Nd(III) in an ionic liquid, triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl) amide ([P2225][TFSA]), was investigated on an electrochemical quartz crystal microbalance (EQCM) at elevated temperatures. Cyclic voltammetry with EQCM measurements of Nd(III) in [P2225][TFSA] at 363, 373 and 378K were performed. A clear cathodic peak with increasing mass and decreasing ηρ (where η is the viscosity and ρ is the density) was observed at −2.79V. Considering the results of our previous investigations, this peak indicated the reduction of Nd(III) to Nd(0) as [Nd(III)(TFSA)5]2−+3e−→Nd(0) + 5[TFSA]−. In addition, the apparent molar mass, Mapp, between −2.49 and −2.94V calculated from the mass change was 140.4gmol−1, which was close to the theoretical value for the electrodeposition reaction of Nd(III)/Nd(0), 144.2gmol−1.Moreover, controlled potential electrolysis with EQCM (CPE/EQCM) measurements at −3.20V was performed for 0.05 and 0.10M Nd(III) in [P2225][TFSA] at 373K. The calculated Mapp values in 0.05 and 0.10M Nd(III) in the initial stage of CPE/EQCM analysis were 147.3 and 148.8gmol−1, respectively, which were close to the theoretical value for reduction of Nd(III) to Nd(0), 144.2gmol−1; thus, electrodeposition of Nd(0) metal was also proved by the CPE/EQCM analysis. Furthermore, energy-dispersive X-ray and X-ray photoelectron spectroscopy analyses of the blackish electrodeposits obtained by the CPE/EQCM measurements were identified as primarily metallic neodymium because the Nd 3d5/2 spectrum was detected within 980.5–981.5eV.