The work presented focuses on the development and performance evaluation of Ni-YSZ (nickel-yttria-stabilized zirconia) supported solid oxide cell with bi-layered ScSZ/GDC electrolyte structure and LSCF (lanthanum strontium cobalt ferrite) oxygen electrode in high-temperature steam and carbon dioxide electrolysis. At 800 degrees C, the cell exhibited a very high electrolysis current density of about -2.2 A/cm(2) and -1.9 A/cm(2) in steam and CO2 electrolysis, respectively. A slightly lower ASR (area specific resistance) is observed in electrolysis mode when compared to fuel-cell mode. Moreover, the ASR is increased when increasing the CO2 concentration in both modes of operation. The OCV (open circuit voltage) of SOEC with bi-layered electrolyte structure is significantly improved than the cell with single-layered GDC (gadolinium-doped ceria) electrolyte but at the cost of an increase in the ohmic resistance (R-s) of cell. The formation of (Zr, Ce)O2-x solid solution by the mutual diffusion of zirconium and cerium during co-sintering is found to be the origin of the increase in the Rs. Impedance spectra revealed that the high electrolysis performance is caused by the low polarization losses at LSCF oxygen electrode rather than the thin bi-layered ScSZ/GDC electrolyte structure. (C) 2015 Elsevier Ltd. All rights reserved.