Electrochimica Acta 89 (2013) 144–151 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al h om epa ge: www.elsevier.com/locate/electacta The direct dissolution of Ce 2 (CO 3 ) 3 and electrochemical deposition of Ce species using ionic liquid trimethyl-n-butylammonium bis(trifluoromethanesulfonyl)imide containing bis(trifluoromethanesulfonyl)imide David W. Hatchett ∗ , Janelle Droessler, John M. Kinyanjui, Beatriz Martinez, Kenneth R. Czerwinski Department of Chemistry, University of Nevada, Las Vegas, 4505 Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, United States a r t i c l e i n f o Article history: Received 31 May 2012 Received in revised form 18 October 2012 Accepted 20 October 2012 Available online 16 November 2012 Keywords: Cerium Dissolution Ionic liquid Deposition a b s t r a c t Ionic liquids (ILs) are solutions comprised of cation/anion pairs that are not limited by the electro- chemical side reactions common to aqueous solution. The high stability of the ionic liquid provides large potential windows that can encompass the thermodynamic potentials for the reduction of f- elements such as cerium to metal. The direct dissolution of Ce 2 (CO 3 ) 3 ·xH 2 O into the ionic liquid trimethyl-n-butylammonium bis(trifluoromethanesulfonyl)imide [Me 3 NBu][TFSI] using conjugate acid bis(trifluoromethanesulfonyl)imide [HTFSI] is demonstrated. The displacement of carbonate ligand and formation of carbonic acid facilitates the in situ dissolution. The subsequent coordination of Ce with the TFSI ion in the IL is monitored using UV/vis spectroscopy and emergent ligand to metal transitions below 300 nm. Further evidence of the coordination of Ce in the ionic liquid is based on changes in the IR spectra for absorbance bands related to the sulfonyl functional groups of the TFSI anion. The reduction/oxidation of soluble Ce in IL is examined at Au, Pt, and GC (glassy carbon) electrodes. Multi-wave voltammetry at all three electrodes is consistent with the reductive deposition of Ce species from the IL solution. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) confirm the deposition of Ce species at mica/Au electrodes. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction A great deal of experimental effort has been devoted to elu- cidating the electrochemistry of the Ce(III)/Ce(IV) redox couple relative to the side reactions in aqueous solutions [1–8]. The stud- ies demonstrate that the solution and electrochemical parameters for common working electrodes including Au, Pt, and GC do not produce fully reversible oxidation/reduction of the Ce(III)/Ce(IV) couple and the deposition of Ce species was not achieved. The research approach highlights the difficulties that exist with respect to defining a universal, optimum working electrode and the solution conditions required to evaluate the oxidation/reduction processes of lanthanide species in aqueous solutions. The potential window in aqueous solutions at positive potential is constrained by water oxidation or metal oxide formation. Hydrogen evolution at negative potentials at both Pt and Au metal surfaces influences the negative potential limit achievable for the reduction of electropositive lanthanides in water. Thus, the ∗ Corresponding author. Tel.: +1 702 895 3509; fax: +1 702 895 4072. E-mail address: david.hatchett@unlv.edu (D.W. Hatchett). ultimate electrochemical window that can be utilized in aqueous solution is 1.3–2.5 V depending upon the electrode composition and the potential constraints based on the side reactions [9–11]: PtO2 + 4H + + 4e - ⇋ Pt(s) + 2H2O E ◦ = 0.83 V versus Ag/AgCl (1) Au2O3 + 6H + + 6e - ⇋ 2Au(s) + 3H2O E ◦ = 0.90 V versus Ag/AgCl (2) O 2 + 4H + + 4e - ⇋ 2H 2 O E ◦ = 1.03 V versus Ag/AgCl (3) 2H + + 2e - ⇋ H 2 E ◦ = -0.20 V versus Ag/AgCl (4) The potentials required for the reduction of Ce in aqueous solu- tion are provided for comparison [12]: Ce 4+ + e - ⇋ Ce 3+ E ◦ = 1.523 V versus Ag/AgCl (5) Ce 3+ + 3e - ⇋ Ce 0 E ◦ = -2.537 V versus Ag/AgCl (6) The reduction of Ce 3+ to metal in aqueous solution is inhibited by hydrogen evolution at negative potential for Au and Pt elec- trodes. In contrast, the oxidation/reduction of lanthanides at Hg electrodes in aqueous solution and the formation of stable amal- gams have been demonstrated [13–17]. The evolution of hydrogen is less thermodynamically favorable at Hg electrodes facilitating the reduction of metals ions and the formation of stable amalgams 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.10.083