Electrochemical synthesis of Sm-Cu dendritic metal catalysts by Co-reduction of Sm(III) and Cu(II) in LiCl-KCl-SmCl3-CuCl2 melt

Abstract

Herein, we report a feasible and rapid route for the preparation of Sm-Cu intermetallic compounds used as an effective metal catalyst. The electrochemical processes of the co-reduction of Sm(III) and Cu(II) ions on Mo electrode or copper-coated Mo electrode in molten LiCl-KCl-CuCl2-SmCl3 system at 873 K were explored. The electrochemical behaviors of Sm(III), Cu(II) ions and intermetallic compounds formation in the melt were investigated by cyclic voltammetry (CV), chronopotentiometry, square wave voltammetry (SWV) and open-circuit chronopotentiometry (OCP), respectively. Our studies showed that the reduction of Cu(II) ions to Cu(0) metal involves two electrochemical steps, Cu(II)/Cu(I) and Cu(I)/Cu(0). Subsequently, Sm-Cu intermetallic compounds (SmCu6, SmCu5 and SmCu) were synthesized by a potentiostatic electrolysis method. As the electrode potential becomes increasingly negative, the formation of Sm-Cu intermetallic compounds gradually changes from Cu-rich side phases (SmCu6) to Sm-rich side phases (SmCu) with Sm-Cu alloys formed as single-crystal intermetallics. The crystal structures of Sm-Cu intermetallic compounds were characterized by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Moreover, the morphology and chemical state of the constituting elements were investigated by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) analyses and X-ray photoelectron spectroscopy (XPS). The dendritic formation of Sm-Cu intermetallic compounds was characterized through nitrogen adsorption-desorption isotherms analysis. The formed Sm-Cu alloys contain hierarchical mesopores with different identified types of mesoporosity. The surface areas of SmCu6, SmCu5 and SmCu calculated from Brunauer-Emmett-Teller (BET) equation were 2.798 m2/g, 3.801 m2/g, 1.688 m2/g, respectively.