Study of phase stability of SrTi0.3Fe0.7O3−δ perovskite in reducing atmosphere: Effect of microstructure

SANTAYA, MARIANO; TOSCANI, LUCIA; BAQUÉ, LAURA; TROIANI, HORACIO E.; MOGNI, LILIANA

SOLID STATE IONICS

ELSEVIER SCIENCE BV

Año: 2019 vol. 342

0167-2738

Increasing SOFC electrode´s surface area by modification of its microstructure is a well-known technique toreduce electrode polarization resistance. This is because reduced grain size and increased porosity promotediffusion and surface reactions, thus improving the electrode performance. However, a modified microstructurealso causes differences in phase stability and in chemical compatibility with other SOFC materials.In this work, we study the effect of particle size in both the electrode performance and the phase stabilityunder different fuel conditions and temperatures. SrTi0.3Fe0.7O3−δ (STF) is both prepared via solid state reaction(STF-SSR) and also by an alternative sol-gel route (STF-SG). The sintering temperature is reduced dramaticallywith the sol-gel method, hence inducing a higher porosity and a much smaller grain size. As particle size isreduced the stability under fuel conditions is also diminished, so decomposition induced by segregation ofmetallic Fe and SrO occurs at lower temperatures for the STF-SG sample. The stability under reducing conditionsis studied by combined techniques such as TGA, TPR, XRD, SEM and TEM. Performance as anode and cathode isevaluated by Electrochemical Impedance Spectroscopy (EIS) by using electrolyte supported symmetrical cells.Prior to electrochemical experiments, the reactivity between La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) electrolyte and STFwas studied, and also between STF and a Lanthanum Doped Ceria (LDC) buffer layer. It is seen that microstructurealso plays a key role in the chemical stability of the STF. The impact of particle size reduction is higherfor the anodic polarization resistance, which is reduced twice from STF-SSR to STF-SG.