Electrochemical Performance of Ni-YSZ, Ni/Ru-GDC, LSM-YSZ, LSCF and LSF Electrodes for Solid Oxide Electrolysis Cells

Abstract

The electrochemical performance of solid oxide electrolysis cells (SOECs) having nickel – yttria stabilized zirconia (Ni-YSZ) hydrogen electrode and a composite lanthanum strontium manganite – YSZ (La0.8Sr0.2MnO3−δ – YSZ) oxygen electrodes has been studied over a range of operating conditions temperature (700 to 900°C). Increasing temperature significantly increased electrochemical performance and hydrogen generation efficiency. Durability studies of the cell in electrolysis mode were made over 200 h periods (0.1 A/cm2, 800°C, and H2O/H2 = 70/30). The cell significantly degraded over the time (2.5 mV/h). Overpotentials of various SOEC electrodes were evaluated. Ni-YSZ as a hydrogen electrode exhibited higher activity in SOFC mode than SOEC mode while Ni/Ru-GDC presented symmetrical behavior between fuel cell and electrolysis mode and gave lower losses when compared to the Ni-YSZ electrode. All the oxygen electrodes gave higher activity for the cathodic reaction than the anodic reaction. Among the oxygen electrodes in this study, LSM-YSZ exhibited nearest to symmetrical behavior between cathodic and anodic reaction. Durability studies of the electrodes in electrolysis mode were made over 20–70 h periods. Performance degradations of the oxygen electrodes were observed (3.4, 12.6 and 17.6 mV/h for LSM-YSZ, LSCF and LSF, respectively). The Ni-YSZ hydrogen electrode exhibited rather stable performance while the performance of Ni/Ru-GDC decreased (3.4 mV/h) over the time. This was likely a result of the reduction of ceria component at high operating voltage.