Effects of strontium doping on oxygen reduction kinetics in thin-film LSCF cathodes

Thesis (M.S.)--Boston UniversityDense films of the mixed ionic-electronic conductor lanthanum strontium cobalt fenite (La1-xSrxCo0.2Fe0.8O3-δ) with x= 0.4, 0.3 and 0.2 (thereafter refened to as LSCF-6428, LSCF-7328 and LSCF-8228) were deposited in fixed patterns on yttria-stabilized zirconia (YSZ) substrates on top of a gadolinium-doped ceria (GDC) barrier layer by pulsed laser deposition (PLD) at the Pacific Northwest National Laboratory (PNNL) in Richland, WA. A counter electrode of porous 50-50 wt %/48.3-51.7 vol.% LCMIYSZ was screen-printed on the opposite side of the substrates. Electrochemical impedance spectroscopy (EIS) data were gathered for each of the compositions in air, but at varying temperatures (600, 700 and 800 °C). The total electrode polarization resistance, Rpob was plotted as a function of composition and temperature. Results show that, for all temperatures, the total polarization resistance drops considerably when the Sr composition is reduced from 0.4 to 0.3, and then increases slightly as the Sr composition is further reduced from 0.3 to 0.2 The relatively high polarization resistance for LSCF-6428 may be explained by recent evidence found by other members of our research group of surface strontium migration in LSCF-6428 films, which results in the formation of phases that could potentially affect electrochemical performance