We observe the electrochemical formation of a silicon layer on a molybdenum (Mo) electrode at 850 degrees C in a CaCl2 melt containing silicon oxide (SiO2) nanoparticles (NPs). A stable electrochemical cell for high temperature molten salt was fabricated from a sealed quartz tube, with a glassy carbon counter electrode and a Ca/Ca2+ dynamic reference electrode. When SiO2 NPs are added into the CaCl2 melt, the reduction current and the generation of a new redox couple relating to the reduced silicon were observed in a cyclic voltammogram at Mo. Spectroscopic analyses confirmed the formation of a silicon layer from the reduction of SiO2 NPs. Although the deposit was not continuous, XPS shows that it is silicon of good purity and XRD shows the pattern of crystalline silicon. We also investigated the dissolved silicon species generated after the oxidation of electrodeposited silicon in CaCl2 melt, which produces a redox couple at potentials positive of the deposition potential. We tentatively attribute it to the oxidation and re-reduction of an insoluble Si-Cl surface species. (C) 2012 Elsevier Ltd. All rights reserved.