A novel thick-film electrolyte-supported cell is constructed to separate cathodic (fuel electrode) from anodic (air electrode) polarization resistance Rp under high electrolysis current in a solid oxide electrolysis cell (SOEC). Rp of the SOEC are measured in various fuel humilities (40, 60, 80% H2O + balance H2) at temperature of 650–800 °C and also compared those of a solid oxide fuel cell (SOFC). Anodic Rp of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) is ∼3 times larger than cathodic Rp of Ni-YSZ (yttria-stabilized zirconia) composite at all temperatures tested, so anodic polarization is the limiting factor of electrolysis performance. Degradation of polarization resistance also occurs mostly at the anode under electrolysis current (−800 mA/cm2). •A new design of a solid oxide cell to separate electrode polarization resistance.•Polarization of anode and cathode is compared with humidities (40–80% H2O).•Polarization of anode is dominant at all temperature (650–800 °C) and humidities.•Air electrode (anode) degraded during electrolysis.