Cyclic voltammetric studies of nitrato complexes of various metal ions in molten LiNO 3 + KNO 3 at 180°C

Abstract

The metal ions investigated on platinum electrodes in the LiNO 3 + KNO 3 melt at 180°C include MN 2+, CO 2+, Ni 2+, Cu 2+, Pt 2+, Fe 2+, Fe 3+, Au 3+, Al 3+, Sc 3+, La 3+, Pr 3+, Nd 3+, Sm 3+, Eu 3+, Gd 3+, Tb 3+, Yb 3+, Ce 3+, and Ce 4+. Additions of these metal ions (0.020 mol kg −1 to the nitrate melt gave increased cathodic currents in the form of new waves or peaks. the cyclic voltammetric studies suggest that nitrato complexes of the transition metal ions are reduced in irreversible electrochemical reactions that form the metal oxide and nitrite ions, i.e, (MONO 2) + + 2 e − → MO + NO − 2 for divalent metal ions. Unusual electrochemical reactivity was observed for Co 2+ and Cu 2+ additions to molten LiNO 3+ + KNO 3 that suggests the release of NO 3 radicals from strongly coordinated nitrate groups. For La 3+ and most other lanthanide metal ions, the nitrato complex is apparently reduced to form the oxide nitrate, e.g., LaONO 3. Reactions of Ce 3+ in the LiNO 3 + KNO 3 melt differ from other lanthanide ions in that they involve the oxidation of Ce(III) to Ce(IV). The reversible electrochemical reduction of Ce(IV) was not apparent in the LiNO 3 + KNO 3 melt.