title: Oxygen sorption and desorption properties of selected lanthanum manganites and lanthanum ferrite manganites.
abstract: Temperature-programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid-oxide fuel cell (SOFC) cathode materials (La(0.85) Sr(0.15)0.95 MnO(3+δ) (LSM) and La(0.60) Sr(0.40) Fe(0.80) Mn(0.20) O(3-δ) (LSFM). The powders were characterized by X-ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second-order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate-determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re-adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order.
authors.affiliation: Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde (Denmark). jini@dtu.dk.
authors.forename: Jimmi
authors.initials: J
authors.lastname: Nielsen
authors.affiliation: Institute of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark Odense, Campusvej 55, DK-5230 Odense M. (Denmark).
authors.forename: Eivind M
authors.initials: EM
authors.lastname: Skou
authors.affiliation: Department of Chemistry, Technical University of Denmark, DK-2800 Lyngby (Denmark).
authors.forename: Torben
authors.initials: T
authors.lastname: Jacobsen
keywords: chemisorption; fuel cells; perovskites; strontium-doped lanthanum manganite; temperature-programmed desorption