A bottom-up building process of nanostructured La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) electrodes for symmetrical-solid oxide fuel cell: Synthesis, characterization and electrocatalytic testing

摘要

Pure-phase La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) (LSCM) nanocrystallites have been successfully synthesized by the combustion method, employing glycine as fuel and complexing agent, and ammonium nitrate as combustion trigger. A detailed morphological and structural characterization is performed, by using of X-ray diffraction, N_2 physisorption and electron microscopy. The LSCM material consists in interconnected nanocrystallites (～30 nm) forming a sponge-like structure with meso and macropores, being its specific surface area around 10 m~2 g~(-1). Crystalline structural analyses show that the LSCM nanopowder has trigonal/rhombohedral symmetry in the R-3c space group. By employing the spin coating technique and quick-stuck thermal treatments of the ink-electrolyte, electrodes with different crystallite size (95,160 and 325 nm) are built onto both sides of the La_(0.8)Sr_(0.2)Ga_(0.8)Mn_(0.2)O_(3-δ)-disk electrolyte. To test the influence of the electrode crystallite size on the electrocatalytic behavior of the symmetrical cells, electrochemical impedance spectroscopy measurements at 800 ℃ were performed. When the electrode crystallite size becomes smaller, the area specific resistance decreases from 3.6 to 1.31 Ω cm~2 under 0.2O_2 -0.8Ar atmosphere, possibly due to the enlarging of the triple-phase boundary, while this value increases from 7.04 to 13.78 Ω cm~2 under 0.17H_2-0.03H_2O-0.8Ar atmosphere, probably due to thermo dvnamic instability of the LSCM nanocrvstallites.