Formation of Si Nanowires by Electro-reduction of Porous Ni/SiO2 Blocks in Molten CaCl2

Electroreduction of porous SiO₂ in molten CaCl₂ is a promising approach to prepare silicon nanowires (SiNWs) in large quantities. However, it is difficult to control the morphologies and surface topologies of the produced SiNWs. In this work, pure nickel metal powders are added into SiO₂, and SiNWs with straight morphology are prepared by electroreduction of solid Ni/SiO₂ blocks in molten CaCl₂ in a wide temperature range. The prepared SiNWs have a diameter distribution of 80 to 350nm, and nickel silicide is found at the tip of the nanowire. Cyclic voltammograms indicate that nickel does not change the mechanism of electrochemical reduction of SiO₂.  The growth process of SiNWs is investigated by XRD, FESEM, HRTEM, EDS, and SAED. It is confirmed that nano-sized nickel-silicon droplets formed at the Ni/SiO₂/CaCl₂ three-phase interface lead the growth of SiNWs, and adding nickel metal into SiO₂ can promote the growth of straight nanowires during the electroreduction of Ni/SiO₂ in molten CaCl₂.