Electrolytic Reduction of Cerium Oxide

Abstract Since the early 2000s, when the Fray-Farthing-Chen (FFC, direct reduction) and the Ono-Suzuki (OS, indirect reduction) processes on titanium oxide were elucidated, several additional metal oxides (Zr, Ta, Cr, and Nb) have been reported to electrolytically reduce to their metallic state in molten CaCl 2 -CaO. 1-3 However, the electrolytic reduction of cerium oxide has resulted in mixed degrees of success. As such, the goal of this study is to identify side reactions that occur that are parasitic to the overall reaction of producing cerium metal and correlate that to the composition of the salt. Previous reports indicate that the reaction pathway from CeO 2 to Ce 0 is not direct and includes side reactions that result in the formation of Ce 2 O 3 , CeOCl and CeCl 3 . 3-5 Our efforts to use cyclic voltammetry to identify side reactions, which allowed for the determination of approximate concentrations of side reaction products as well as Ce 0 produced as a result of electrolysis, will be presented. Acknowledgements For financial support of this work, we acknowledge the U.S. Department of Energy through the LANL LDRD Program (Mission Foundations Research Project #20170558ER). References 1 Chen, G. Z., Fray, D. J. & Farthing, T. W. Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride. Nature 407 , 361-364 (2000). 2 Suzuki, R. O., Ono, K. & Teranuma, K. Calciothermic reduction of titanium oxide and in-situ electrolysis in molten CaCl 2 . Metallurgical and Materials Transactions B 34 , 287-295, (2003). 3 Claux, B., Serp, J. & Fouletier, J. Electrochemical reduction of cerium oxide into metal. Electrochimica Acta 56 , 2771-2780, (2011). 4 Zhao, B. et al. Direct electrolytic preparation of cerium/nickel hydrogen storage alloy powder in molten salt. Journal of Alloys and Compounds 468 , 379-385, (2009). 5 Castrillejo, Y., Bermejo, M. R., Pardo, R. & Martı́nez, A. M. Use of electrochemical techniques for the study of solubilization processes of cerium–oxide compounds and recovery of the metal from molten chlorides. Journal of Electroanalytical Chemistry 522 , 124-140, (2002).