resumo
Effects of iron doping on the functional properties of (La,Sr)CrO3-based electrode materials have been appraised in a range of conditions relevant for SOFCs and other electrochemical applications. Mossbauer spectroscopy of perovskite-type (La0.75Sr0.25)(0.95)Cr1-x O3-delta (x=0.3-0.4), combined with thermogravimetry and X-ray diffraction, shows that the prevailing oxidation state of iron cations in both oxidizing and reducing atmospheres remains 3+. The redox behavior and transport properties are, therefore, essentially governed by Cr3+/4+ couple, leading to dominant p-type electronic conduction in the oxygen partial pressure range from 0.5 down to 10(-20) atm at 973-1223 K. The total conductivity and Seebeck coefficient variations indicate that the electronic transport decreases with iron additions as the hole concentration and mobility become lower. The partial ionic conductivity estimated from the steady-state oxygen permeability under air/H-2-H2O-N-2 gradients is 0.05-0.08 S cm(-1) at 1223 K and p(O-2)= 10(-17) atm, and increases with x due to rising oxygen deficiency. A similar tendency was observed for chemical expansion studied by the controlled-atmosphere dilatometry, whereas the average thermal expansion coefficients are almost independent of x and vary from 11.1-11.3 x 10(-6) K-1 in air down to 10.3-10.5 x 10(-6) K-1 in CO-CO2 at 350-1370 K. The electrochemical activity of porous (La0.75Sr0.25)(0.95)Cr0.7Fe0.3O3-delta anodes with Ce0.8Gd0.2O2-delta interlayers, applied onto LaGaO3-based solid electrolyte, is higher compared to (La(0.7)sSr(0.25))(0.95)Cr0.5Mn0.5O3-delta when no metallic current-collecting layers are used. Increasing iron content lowers the electrode performance in wet H-2-containing atmospheres, in correlation with electronic conduction. (C) 2012 Elsevier B.V. All rights reserved.
palavras-chave
OXIDE FUEL-CELLS; OXYGEN NONSTOICHIOMETRY; ELECTRODE MATERIALS; REACTION-MECHANISMS; MIXED CONDUCTIVITY; METHANE OXIDATION; MOSSBAUER-SPECTRA; INDUCED EXPANSION; DEFECT STRUCTURE; COMPOSITE ANODE
categoria
Chemistry; Electrochemistry; Energy & Fuels; Materials Science
autores
Lu, MF; Tsipis, EV; Waerenborgh, JC; Yaremchenko, AA; Kolotygin, VA; Bredikhin, S; Kharton, VV
nossos autores
Aleksey Yaremchenko
Investigador Principal
Vladislav Kharton
Investigador Principal CovidadoProjectos
agradecimentos
This work was partially supported by the FCT, Portugal (projects PTDC/CTM/64357/2006, PTDC/CTM-CER/114561/2009, SFRH/BPD/28629/2006 and SFRH/BD/45227/2008), and by the Ministry of Education and Science of the Russian Federation (state contract 02.740.11.5214).