Electrochemical Characteristics of Sr(Ti0.3Fe0.7)O3-Based Electrodes in Solid Oxide Cells Operated in H2/H2O and CO/CO2 Mixtures

The electrochemical characteristics of SrTi0.3Fe0.7O3-delta (STF), Sr0.95Ti0.3Fe0.63Ni0.07 O3-delta (STFN), and Sr0.95Ti0.3Fe0.63Ru0.07 O3-delta (STFR) fuel electrodes were compared for a range of H2/H2O and CO/CO2 fuel mixtures. Electrodes prepared in symmetrical solid oxide cells were measured using impedance spectroscopy over a range of temperatures. Impedance spectra were fitted well in all cases using an equivalent circuit that featured three R-Q elements, but the response was generally dominated by a low frequency process associated with adsorption and charge transfer. The electrodes all yielded similar polarization resistances RP values at relatively high temperature (>= 800 degrees C) in H2/H2O, but STFN and STFR were substantially better than STF at lower temperatures. STFR yielded a much lower RP than the other electrodes when operating in CO/CO2. In full cells with these electrodes, STFR-based cells yielded superior power density and smaller polarization resistance compared to both STFN and STF cells, consistent with the symmetric cell results. It is suggested that the superior performance of STFR in CO/CO2 resulted from an enhancement of electrode processes in the presence of exsolved Ru-Fe nanoparticles.