New SOFC electrode materials: The Ni-substituted LSCM-based compounds (La 0.75Sr 0.25)(Cr 0.5Mn 0.5 − xNi x)O 3 − δ and (La 0.75Sr 0.25)(Cr 0.5 − xNi xMn 0.5)O 3 − δ

Abstract

New compounds based on the perovskite LSCM (La 0.75Sr 0.25) (Cr 0.5Mn 0.5)O 3 − δ , have been developed. The partial substitution of Mn or Cr by Ni in LSCM has been studied and single phases were obtained under air and different reducing atmospheres. The limit of solid solution was 20% of nickel in B site. As confirmed by TEM, a partial exsolution of Ni is obtained from the reduction of LSCM nickel-substituted compounds. In all cases the substituted phases show conductivities slightly higher than those corresponding to the undoped materials. The total conductivity seems to be mainly p-type and the substitution with Ni essentially affects the Mn 3+/Mn 4+ valence ratio. The lower conductivities obtained under reducing atmosphere should be related to the reduction of manganese. Nevertheless the obtained conductivities are high under both atmospheres and suitable for the application of these materials as electrodes in a SOFC. A suggestive protonic contribution to the total conductivity is observed under H 2 between 300 °C and 500 °C. The existence of nanoparticles of Ni at the chromo-manganite crystallites surface due to Ni exsolution process could facilitate the hydrogen dissociation promoting a protonic contribution to total conductivity. The activity and selectivity of LSCMMn 0.30Ni 0.20 toward the total oxidation of methane were studied and compared to those of LSCM. LSCMMn 0.30Ni 0.20 selectively catalyzes the complete oxidation of methane as required for a SOFC electrode.