Sr2FeNbO6 Applied in Solid Oxide Electrolysis Cell as the Hydrogen Electrode: Kinetic Studies by Comparison with Ni-YSZ

Double-perovskite Sr2FeNbO6 (SFN) has been introduced to the solid oxide electrolysis cell (SOEC) supported by 8 mol% yttria stabilized zirconia (YSZ) electrolyte (500 μm thick) with the cell composition of SFN-YSZ/YSZ/LSM-YSZ (La0.8Sr0.2MnO3, LSM). Five groups of contrast tests are designed to investigate the differences between SFN and Ni in electrochemical behavior. The reaction mechanisms of the H2O reduction in Ni-YSZ and SFN-YSZ electrodes are discussed. The results show that the conductivity of SFN in H2/H2O (80 vol% H2O) atmosphere (2.215 S cm−1 at 850 °C) is much higher than that in air (0.049 S cm−1 at 850 °C). The electrochemical impedance spectroscopy (EIS) measurement results indicate that, compared with Ni-YSZ, SFN-YSZ is more suitable for high temperature steam electrolysis as the hydrogen electrode. X-ray photoelectron spectroscopy (XPS) analysis suggests that the surface of SFN can also be one of the electrode reaction places besides the triple phase boundary (TPB), which greatly accelerates the reaction process, lowers the energy barrier of the charge transfer process and results in a better performance of SFN-YSZ than Ni-YSZ in the SOEC mode.