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Voltammetric behavior of some light lanthanide ions (La3+, Pr3+, Nd3+, Sm3+, and Eu3+) in various supporting electrolytes has been investigated by several electrochemical techniques. The peak potentials and the peak currents, their dependency on the concentration, temperature and pH effects, the reversibility of the electrode reactions are described. The reduction of La3+, Pr3+ and Nd3+ in 0.1 M lithium chloride proceeds by a three-electron change directly to the metallic state (Ln3+ ＋ 3e- → Ln0) and charge transfer is totally irreversible. However, the reduction of Sm3+ in 0.1 M tetramethylammonium iodide and Eu3+ in 0.1 M lithium chloride proceeds in two stages (Ln3+ ＋ e- → Ln2+ and Ln2+ ＋ 2e- → Ln0). At pH values lower than ca.4 the hydrated lanthanide species (Ln(OH)2+) reduced before the lanthanide ions (Ln3+) due to the catalytic effect of hydrogen ions, and peak current increase with in the order Eu3+ < Sm3+ < Nd3+ < Pr3+ < La3+ in differential pulse polarography. Some representative plots of ipcV-1/2 (proportional to current function) vs. V show considerable influence of hydrogen ion/lanthanide ion concentration in cyclic voltammetry. It is shown that a reaction of lanthanide ions with proton and/or water and catalytic reaction is enhanced at lower pH and at decreased lanthanide ion concentration.
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