The ability to control the degree of supersaturation using electric potential in electrochemical nucleation and growth is generally limited to studies in metal electrodeposition and electrochemical oxide formation. Here we report in-situ observations of 2D crystal nucleation and thin layer growth during the solid state electro-deoxidation of TiO2 in CaCl2 melt. The nucleation mechanism is found to be progressive-like according to the non-dimensional Scharifker-Hill model where relatively slow Ti nucleation occurs on a large number of active sites. After the formation of a thin layer, changing the design of the porous cathode or inert anode has a profound effect on the rate and distribution of electro-deoxidation on the Ti/TiO2/melt three-phase interline. (C) 2016 Elsevier Ltd. All rights reserved.