resumo
Increasing Sr2+ and Ti4+ concentrations in perovskite-type (La0.75-xSr0.25+x)(0.95)Mn0.5Cr0.5-xTixO3-delta(x - 0 - 0.5) results in slightly higher thermal and chemical expansion, whereas the total conductivity activation energy tends to decrease. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range (10.8-14.5) x 10(-6) K-1 at 373-1,373 K, being almost independent of the oxygen partial pressure. Variations of the conductivity and Seebeck coefficient, studied in the oxygen pressure range 10(-18)-0.5 atm, suggest that the electronic transport under oxidizing and moderately reducing conditions is dominated by p-type charge carriers and occurs via a small-polaron mechanism. Contrary to the hole concentration changes, the hole mobility decreases with increasing x. The oxygen permeation fluxes through dense ceramic membranes are quite similar for all compositions due to very low level of oxygen nonstoichiometry and are strongly affected by the grain-boundary diffusion and surface exchange kinetics. The porous electrodes applied onto lanthanum gallate-based solid electrolyte exhibit a considerably better electrochemical performance compared to the apatite-type La10Si5AlO26.5 electrolyte at atmospheric oxygen pressure, while Sr2+ and Ti4+ additions have no essential influence on the polarization resistance. In H-2-containing gases where the electronic transport in (La0.75-xSr0.25+x)(0.95)Mn0.5Cr0.5-x TixO3-delta perovskites becomes low, co-doping deteriorates the anode performance, which can be however improved by infiltrating Ni and CeO(2-delta)v into the porous oxide electrode matrix.
palavras-chave
OXIDE FUEL-CELLS; ELECTRICAL-PROPERTIES; ELECTROCHEMICAL-BEHAVIOR; LANTHANUM MANGANITES; OXYGEN PERMEABILITY; REACTION-MECHANISMS; DIRECT OXIDATION; COMPOSITE ANODE; CONDUCTIVITY; TEMPERATURE
categoria
Electrochemistry
autores
Kolotygin, VA; Tsipis, EV; Shaula, AL; Naumovich, EN; Frade, JR; Bredikhin, SI; Kharton, VV
nossos autores
Jorge Ribeiro Frade
Professor Catedrático
Vladislav Kharton
Investigador Principal Covidadoagradecimentos
This work was partially supported by the FCT, Portugal (projects PTDC/CTM/64357/2006, SFRH/BD/45227/2008, SFRH/BPD/28629/2006, and SFRH/BPD/28913/2006), by the European Commission (project STRP 033410-MatSILC), and by the Ministry of Education and Science of the Russian Federation (state contract 02.740.11.5214).