MIEC Materials for Membrane Applications: Enhancing the Oxygen Transport

摘要

Mixed ionic-electronic conducting (MIEC) materials are of great interest for a variety of high-temperature applications, such as dense ceramic oxygen transport membranes (OTMs) for gas separation. Several MIEC perovskite oxides, e.g., Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ), La_(0.58)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ), or La_(0.6)Sr_(0.4)CoO_(3-δ) exhibit excellent oxygen-ionic and electronic transport properties and are, hence, promising candidates for high-permeation OTMs. It is essential, though, to determine their chemical stability and electrochemical transport properties (D~δ and k~δ) over a broad range of oxygen partial pressure pO_2 first. This can both be achieved in a custom-made zirconia "oxygen pump" setup. Surface oxygen exchange (k~δ) becomes rate-determining for oxygen permeation of high-performing thin OTMs. Further increase of oxygen flux requires an enhancement of surface exchange. This can be achieved by modifying the OTM surfaces with a porous functional layer. With the help of a 3D FEM OTM model the inter-play of transport parameters and functional-layer microstructure (thickness, porosity, particle sizes) can be readily assessed.