INVESTIGADORES
BAQUE Laura Cecilia
congresos y reuniones científicas
Título:
Study of phase stability of SrTi0.3Fe0.7O3 perovskite in reducing atmosphere: effect of microstructure
Autor/es:
MARIANO SANTAYA; LAURA BAQUÉ; LUCÍA TOSCANI; DANIEL DRASBAEK; KARIN VELS HANSEN; PETER HOLTAPPELS; HORACIO TROIANI; LILIANA MOGNI
Reunión:
Conferencia; 22nd Internacional Conference on Solid State Ionics SSI-22; 2019
Resumen:
Solid oxide fuel cell (SOFC) anodes composed of electronically conducting perovskites are alternatives to Ni-YSZ anodes that can provide improved tolerance to redox cycling, fuel impurities, and hydrocarbon fuels. SrTi0.3Fe0.7O3 (STF) is gaining relevance because it yields a power density of 1.1 W cm2 at 850 ºC in humidified hydrogen, approaching the values achieved in state-of-the-art Ni-YSZ anodes. However, it is well known that the increases of surface area of electrodes are the clue to reduce electrode polarization resistance, thus being possible to obtain higher power densities at lower temperature. However, it is not clear that in the case of perovskite based anodes this could reduce the stability of the oxide in the fuel atmosphere. In this work, we studied the effect of particle size in either, the anode performance and the thermodynamic stability under the different fuel conditions and temperatures. SrTi0.3Fe0.7O3-δ is both prepared via solid state reaction (STF-SSR) and also by an alternative sol-gel route (STF-SG). The sintering temperature is reduced dramatically with the sol-gel method, this fact inducing a higher porosity and a much smaller grain size. As particle size is reduced the stability under fuel condition is also diminished. STF-SG shows Fe nanoparticles ex-solution at 750°C in a wet 10%H2 atmosphere, while no ex-solution is seen for STF-SSR even under more aggressive reducing conditions (850°C in wet 30%H2). Reduction and re-oxidation cycles are studied for both samples by using combined techniques such as XRD, SEM, TEM and RAMAN. It is seen that STF-SG recovers its original state almost immediately after the reducing atmosphere is changed to oxidizing conditions at 750°C. This suggests that the ex-solution process is easily reversible in STF samples.Anode performances were evaluated by Impedance Spectroscopy as a function of temperature and fuel conditions by using electrolyte supported symmetrical cells. Previously, the reactivity between LSGM electrolyte and the LDC protective layer with STF was analyzed for both preparation methods, because also the microstructure play a role in the chemical compatibility between materials.