abstract
Dense Ce0.8Pr0.2O2-delta ceramic membranes with submicron grain size can be formed at 1000 degrees C by minor additions of cobalt oxide. X-ray energy-dispersive spectroscopy shows the additive to be located in the grain boundary. Although a very fine grain interface is obtained for the composition containing 2 mol % cobalt oxide, pronounced grain boundary layers and Co-rich fringes are noted at 5 mol %. The cobalt oxide additions enhance electronic conductivity by around 2-3 times. For 2 mol % additions, no change to the level or nature of ionic conductivity is observed, whereas at 5 mol %, a depleted ionic conductivity is noted at lower temperatures. Coulombic titration studies show the bulk Pr oxidation state to be unaffected by the additions. Jointly, these results prove that the Co additions are not accommodated in the bulk material but instead form additive-rich grain boundary networks that are electronically conductive. Materials essentially free from oxygen surface exchange limitations are produced on addition of 2 mol % cobalt oxide, in contrast to that noted for 5 mol %. The combination of enhanced ambipolar conductivity and enhanced oxygen surface exchange kinetics boosts oxygen permeability in 2 mol % cobalt oxide doped Ce0.8Pr0.2O2-delta to offer one of the highest levels of oxygen permeability reported to date for a single component mixed conducting fluorite material.
keywords
CERIA SOLID-SOLUTIONS; OXYGEN PERMEABILITY; THERMAL-EXPANSION; MIXED CONDUCTORS; ELECTRICAL-CONDUCTIVITY; ELECTRONIC TRANSPORT; FUEL-CELLS; O SYSTEM; PR; MICROSTRUCTURE
subject category
Chemistry; Materials Science
authors
Fagg, DP; Garcia-Martin, S; Kharton, VV; Frade, JR
our authors
Jorge Ribeiro Frade
Retired Professor
Vladislav Kharton
Invited Principal Researcheracknowledgements
This work was supported by the FCT, Portugal (projects PTDC/CTM/66243/2006, SFRH/BPD/3529/2000, and REEQ/710/CTM/2005). S.G.-M, thanks the Spanish MEC for funding Project MAT2007-64486-C07-04 and CAM for Project MATERYENER S 505/PPQ/0358. The authors also thank the Microscopy Centre Luis Bru from UCM for technical assistance.