Oxygen permeation through the LSCO-80/CeO2 asymmetric tubular membrane reactor

Mixed conductive perovskite materials, e.g., La_1−xSr_xO_3−δ (LSCO), have been widely investigated to understand the leverages of doping extent and composition on the oxygen permeability with the aim of developing an oxygen-transport solid electrolyte membrane. However at the present stage fabrication of a dense thin layer of perovskite oxide on a porous tubular support possessing mechanically and chemically stability at high temperatures is still a technological challenge to the endeavor. This is because the asymmetric configuration is a desired model of the commercial oxygen-permeable ceramic membrane reactor. The present work develops a new approach that allows the formation of a complete gas-tight oxygen-permeable thin membrane on the outer surface of a porous CeO₂ tube by the means of slurry coating. The oxygen-permeable membrane is a dual-phase composite containing equal volume fractions of CeO₂ and LSCO-80 (x = 0.8). In the membrane CeO₂ particles are uniformly embedded in the continuous LSCO phase, and this highly dispersed semi-continuous structure could successfully buffer the mechanical stress generated in the LSCO phase due to mismatch of coefficient of thermal expansion (CTE) between the membrane and the support. The oxygen permeation flux tests showed a low activation energy barrier (∼30 kJ/mol) of the whole electrochemical reaction in the temperature range from 400 to 900 °C. The surface de-sorption (or the anodic) process of the oxygen has been simulated using the extended Hückel theory (EHT). The activation energy obtained from the EHT simulation is found very close to the experiment data. In addition, according to the computer simulation, surface oxygen de-sorption activation energy relies on the surface oxygen vacancy density and thus the oxygen partial pressure.