Abstract
Reversible solid oxide cells (RSOCs) can generate electricity as solid oxide fuel cells (SOFC) facing a shortage of electricity and can also store the electricity as solid oxide electrolysis cells (SOEC) at the time of excessive electricity. The composite Sr0.95Y0.05TiO3-delta-Sm0.2Ce0.8O1.9 (SYT-SDC) as the hydrogen electrode provides a promising alternative for a conventional Ni/YSZ. The possible charge compensation mechanism of SYT is described as Sr0.95Y0.05Ti0.95-2 delta 4+Ti2 delta 10.053+O3-delta. The Ti3+ is approximately 11.73% in the reduced SYT by XRD Rietveld refinement, electron paramagnetic resonance (EPR) and thermogravimetry (TG) analysis. Voltage-current curves and impedance spectra are measured as a function of applied voltages to characterize the cells. The bulk resistance (R-o) and the electrode polarization resistance (R-p) at open circuit voltages (OCV) at 750 degrees C are 9.06 Omega cm(2) and 10.57 Omega cm(2), respectively. The R-o values have a small amount of changes with small slopes both in the SOFC (-0.29 Omega cm(2) V-1) and SOEC mode (0.5 Omega cm(2) V-1), whereas the Rp values decrease all the time with the increasing voltages at both the SOFC (-2.59 Omega cm(2) V-1) and SOEC mode (-9.65 Omega cm(2) V-1), indicating that the electrical conductivity and electro-catalytic property of the SYT-based hydrogen electrode can be improved under the SOEC mode.