Abstract:
Steam electrolysis for hydrogen production is investigated in solid oxide electrolysis cell (SOEC). Sc3+, Ce4+, and Gd3+ are doped in zirconia (SCGZ) and compared with yttria stabilized zirconia (YSZ) and gadolinium doped ceria (GDC) electrolyte. Electrolyte-supported cells are fabricated. The SCGZ and YSZ electrolytes are dense with >95% relative density while GDC is less densified. The activation energy of conduction of the SCGZ electrolyte is the lowest at 65.58 kJ mol-1 although phase transformation is detected after electrolyte fabrication process. Cathode-supported cell having SCGZ electrolyte (Ni-SCGZ/SCGZ/BSCF) shows the highest electrochemical performance. Durability test of the cells in electrolysis mode is carried out over 60 h (0.3 A cm-2, 800 °C, H2O to H2 ratio of 70:30). Significant performance degradation of Ni-GDC/YSZ/GDC/BSCF cell is observed (0.0057 V h-1) whereas the performance of Ni-YSZ/YSZ/BSCF and Ni-SCGZ/SCGZ/BSCF are rather stable under the same operating conditions. The BSCF remains attaching to the SCGZ electrolyte and additional phase transformation is not observed after prolong operation. However, stabilization of high conducting cubic phase by adding 1-2 mol% of Bi2O3 in SCGZ is also investigated. Bi2O3 is found to act as both phase stabilizer and sintering aid. In addition, the ionic conductivity of the electrolyte is also improved with adding Bi2O3.
