The effects of starting material and catalyst on the morphology of produced Si have been investigated for the direct electrolytic reduction of porous SiO2 pellets in molten CaCl2 at 1123 K. The Si nanowires (SiNWs) were produced using amorphous SiO2 pellets with a tetrapod-like microstructure as the starting material, whereas plate-like Si was obtained from pellets made of spherical fumed SiO2. The SiNWs showed irregular branching and a wide distribution of diameters as the electrolysis proceeded. On the other hand, elongated SiNWs were formed during the electrolysis of pellets comprised of Au nanoparticles (AuNPs) and tetrapod-like microstructured SiO2 powder. This suggests that AuNPs work as catalysts for longitudinal nanowire growth in the present electrolytic process. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3575635] All rights reserved.