Synthesis and characterization of pure-phase La0.75Sr0.25Cr0.5Mn0.5O3−δ nanocrystallites for solid oxide fuel cell applications

Nanopowders of La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) perovskite-type oxide, potential electrode material for symmetrical solid oxide fuel cell (S-SOFC), have been successfully prepared by the solution combustion method employing glycine as complexing agent and fuel. Several glycine-to-nitrates molar ratios were investigated. A detailed morphological and structural characterization was performed, employing X-ray diffraction, N2 physisorption, and electron microscopy (scanning and transmission). The as-synthesized LSCM nanopowders consist of interconnected nanoparticles forming a sponge-like structure with typical meso- and macropores. For glycine-to-nitrates molar ratios above stoichiometric molar ratio, a high proportion of well-crystallized LSCM phase was obtained. An increase of glycine content in the initial synthesis gel, decreases the average nanoparticles size from ~20 to ~6 nm, narrows the distribution crystallite size, and increases the specific surface area of the LSCM nanopowders from ~14 to ~30 m2/g. The evolution of crystalline phases of the as-synthesized LSCM nanopowders after calcination at various temperatures was studied: pure-phase La0.75Sr0.25Cr0.5Mn0.5O3−δ perovskites with particle-size distribution between 100 and 300 nm, have been obtained after calcination at 1,000 °C for 6 h. The crystalline structural analyses showed that the LSCM nanocrystallites have trigonal/rhombohedral symmetry in the R-3c space group. These final LSCM nanopowders present microstructures with low densification and open porosity but probably with sufficient integrity to enable them to be used as efficient electrodes in S-SOFC.