Electrochemical codeposition of La and Fe-group metals in a dicyanamide ionic liquid

Abstract

Room-temperature electrochemical deposition of lanthanides and their alloys can be achieved employing organic ionic media, such as ionic liquids (ILs). Here, we study the electrochemical (co)deposition of La and Fe-group transition metals from solutions in 1-butyl-1-methyl-pyrrolidinium dicyanamide IL, [BMP][DCA], with controlled water content. We show that electroreduction of La(III) ions starts in the two-component solutions containing La(III) + Me(II) (Me = Co, Fe, or Ni) and no added water in the same potential interval as the electroreduction of respective Me(II). La is thus codeposited with the respective Fe-group metal, as evidenced by voltammetric, microscopic, and X-ray analyses, at considerably more positive potentials than in a solution containing only La(III) ions. Such a promoting effect is not observed in the presence of Cu(I) and Sn(II). Furthermore, the effect of water on the (co)deposition of La and Fe-group metals is systematically investigated. The La-Me (Me = Co, Fe, or Ni) codeposition is inhibited in the presence of moderate amounts of water (up to 0.32 M). At higher water contents, particularly ≥0.32 M H2O in the La(III) + Ni(II) solution, the electroreduction of La starts at more positive potentials than the deposition of Ni. This allows obtaining La-Ni deposits with a high La content. The XPS data indicate that La is present in the deposits in both metallic and oxidized states, even if deposition occurs in a solution with no added water. The results obtained in this study offer valuable insight into the electro(co)deposition of La from IL solutions and contribute to the progress of techniques for producing lanthanide-based functional coatings.