Porous Scandia-Stabilized Zirconia Layer for Enhanced Performance of Reversible Solid Oxide Cells

Reversible solid oxide cells (RSOCs) developed so far display short-term stability during solid oxide electrolysis cell (SOEC) mode. This is due to the delamination of the strontium-doped lanthanum manganite (LSM) air electrode when tested for a long time. Here, we report a highly stable RSOC operation of LSM for 5 cycles using half and full cells. A scandia-stabilized zirconia (SSZ) porous layer was applied between the dense SSZ electrolyte and the porous LSM electrode. The half-cells were tested under ±0.5 A cm^-2, whereas the full cells were tested at +0.5 and -0.25 A cm^-2 at 800 °C. It was found that the cells with a porous SSZ layer are stable and show a performance increase after five RSOC cycles. The ohmic and polarization resistance of both the half and full cells decreased after each cycle. Also, the maximum power density of the full cell increased from 425 to 550 mW cm^-2, whereas the electrolysis current density increased from 294 to 407 mA cm^-2 after 5 cycles at 1.3 V in 10% H₂O/90% H₂, at 800 °C. This performance enhancement can be ascribed to the creation of oxygen vacancies in LSM under applied current, the alleviation of oxygen partial pressure from the interface and the introduction of electronic conductivity in the electrolyte near the interface. The cell without the SSZ porous layer experienced the zirconate formation, high oxygen partial pressure at the interface as well as the silver deposition at the electrode-electrolyte interface. Therefore, an increase in the polarization resistance for the half-cell and a decrease in the electrolysis current density for the full cell were observed.