Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3-delta membranes
authors Kharton, VV; Tsipis, EV; Marozau, IP; Yaremchenko, AA; Valente, AA; Viskup, AP; Frade, JR; Naumovich, EN; Rocha, J
nationality International
journal JOURNAL OF SOLID STATE ELECTROCHEMISTRY
author keywords perovskite; oxygen membrane; mixed conductor; methane oxidation; electron-hole transport
keywords PEROVSKITE-TYPE OXIDES; OXYGEN NONSTOICHIOMETRY; ION-TRANSPORT; CONDUCTIVITY; METHANE; PERMEABILITY; TRANSITIONS; EXPANSION
abstract Incorporation of gallium into the perovskite lattice of La0.3Sr0.7CoO3-delta leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973 - 1223 K, the oxygen permeation fluxes through La0.3Sr0.7Co0.8Ga0.2O3-delta ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La0.3Sr0.7Co0.8Ga0.2O3-delta, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O-2) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9 x 10(-6) K-1 at 360 - 710 K and 27.9 x 10(-6) K-1 at 710 - 1030 K. On decreasing oxygen pressure down to 4 - 30 Pa at 973 - 1223 K, perovskite-type La0.3Sr0.7Co0.8Ga0.2O3-delta transforms into a brownmillerite-like modi. cation, whose electrical properties are essentially p( O2) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O-2)= 8 x 10(-10) - 3 x 10(-4) Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La0.3Sr0.7Co0.8Ga0.2O3-delta membranes are, however, kinetically stable under an air/CH4 gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO2 concentrations (> 90%), indicating a dominant role of complete CH4 oxidation on the membrane surface.
publisher SPRINGER
issn 1432-8488
year published 2005
volume 9
issue 1
beginning page 10
ending page 20
digital object identifier (doi) 10.1007/s10008-004-0530-0
web of science category Electrochemistry
subject category Electrochemistry
unique article identifier WOS:000225410600002
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journal impact factor 2.509
5 year journal impact factor 2.348
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