Degradation and stabilization of perovskite membranes containing silicon impurity at low temperature

The oxygen permeation flux of a mixed ionic-electronic conducting membrane BaCe0.1Co0.4Fe0.5O3−δ (BCCF) decreased by 62% after 477 h on-stream operation under air/He gradient at 600 °C. To understand this phenomenon, the spent membrane was examined via several characterization techniques. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analyses revealed that the surface of the sweep side has a higher silicon impurity content than that of the feed side. In fact, the BCCF powder contained up to 140 ppm of silicon impurities, which originated from the original chemicals and/or was introduced during preparation of the material. After the 477 h operation at 600 °C, a ~25 nm-thick amorphous silicon-containing layer was detected by high resolution transmission electron microscopy (HRTEM) on the sweep side surface of the spent membrane. A possible mechanism related to silicon migration from membrane bulk to surfaces was proposed to explain the degradation phenomenon. To overcome the negative effects of silicon impurity, a simple and effective method was proposed to stabilize the oxygen permeation fluxes at low temperatures, i.e. coating a porous Sm0.5Sr0.5CoO3−δ (SSC) catalyst on both surfaces of the membrane to accommodate the silicon impurity and accelerate oxygen exchange kinetics. With this method, the oxygen permeation was stabilized for 500 h at 600 °C.