The effect of microstructure and surface decoration with K2NiF4-type oxide upon the oxygen permeability of perovskite-type La0.7Sr0.3FeO3−δ hollow fiber membranes
Dense La0.7Sr0.3FeO3−δ (LSF) hollow fiber membranes with two kinds of microstructures (LSF-a and LSF-b) were prepared by the phase inversion/sintering method. Outer surface decoration with dispersed porous K2NiF4-type oxide (La0.5Sr0.5)2CoO4+δ (LSC214) was employed to improve the surface exchange reaction kinetics of oxygen reduction. Experimental results suggest the oxygen permeability of the LSF-b membrane is much better than that of LSF-a membrane at all the tested conditions, which means the microstructure of the hollow fiber membrane plays a crucial role in the oxygen permeability. LSC214 decoration further increases the oxygen permeation flux greatly. Moreover, although the oxygen permeation fluxes are positively related to both the operating temperature and flow rate of helium gas, the former has a greater effect on the oxygen permeation performance than the latter. Keeping the flow rate of helium gas at 200 ml min−1, the oxygen permeation fluxes of the bare LSF-a (LSF-b) and the LSC214-decorated LSF-a (LSF-b) membranes are about 0.009–0.367 (0.254–5.401) and 0.048–0.426 (1.520–7.003) ml min−1 cm−2, respectively, with operating temperature varied from 700 to 1000 °C. For both kinds of decorated membranes, more remarkable improvements of oxygen permeation fluxes appear at intermediate operating temperature range (700–850 °C) than higher temperature range (850–1000 °C), which indicates that the surface oxygen exchange reaction plays a decisive role in controlling the overall oxygen transport process at lower temperature. In addition, the surface decorated membrane also displays high permeation stability under the investigated operating conditions.