UNIDEF   23986
UNIDAD DE INVESTIGACION Y DESARROLLO ESTRATEGICO PARA LA DEFENSA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
In Situ XAS study of Pr0.6Sr0.4CoO3-d for IT-SOFC cathode application
Autor/es:
FUENTES, R. O.; MUÑOZ, F. F.; ACUÑA, L. M.
Reunión:
Encuentro; 28th RAU - ANUAL USERS MEETING; 2018
Institución organizadora:
CNPEM
Resumen:
Cobaltites are high-temperature mixed ionic and electronic conductors that have been studied for long time as possible cathode materials for solid oxide fuel cell (SOFC) application. The high working temperature (900-1000ºC) of SOFCs requires expensive materials as current collectors and interconnectors and reduces the life span of the device. So, it is necessary to reduce the working temperature to intermediate temperatures in the range of 500-700 ºC (IT-SOFC). In this work, we present an in situ XAS study on Pr0.6Sr0.4CoO3-d (PSC) nanopowders (average crystallite size, D≈30 nm), focused on the speciation of Co atoms under different temperatures and O2(g) concentration in view of their possible application as cathode in IT-SOFCs. PSC was synthesized via the gel-combustion method. In situ XAS studies were performed at the D04B-XAFS-1 beamline of the LNLS. The Co K- Sr K- and Pr L3-edges were measured in transmission mode, from 20 to 700 ºC in controlled atmosphere with different O2(g) concentrations. In situ XPD analysis was performed at the D10B-XPD beamline of the LNLS, under identical experimental conditions. PSC exhibits the orthorhombic phase in the whole temperature range with a possible secondary phase. Pr atoms are in +3 oxidation state, independently of the temperature or O2(g) concentration. The relative amount of cobalt's +2, +3 and +4 oxidation states varied according to temperature and O2 content but cobalt's average oxidation state was invariant, close to +3.2. For comparison, PSC micropowders (D>300 nm) exhibited almost the same average oxidation state as PSC nanopowders, but the relative amounts of Co species were invariant under the different conditions and the Co2+ and Co4+ content was lower. This suggests that the electronic compensation reaction would play an important role in the electrochemical properties of PSC materials and would explain partially the enhanced electrochemical performance of PSC nanopowders when used as IT-SOFC cathode