Effects of hydrogen treatment on the surface microstructure and oxygen permeability of La0.7Sr0.3Ga0.3Fe0.7O3-δ membrane

摘要

A dense La0.7Sr0.3Ga0.3Fe0.7O3-δ membrane tube was treated with hydrogen by exposing its tube side to a H2 stream and the shell side to the ambient air at 950°C. A porous layer of thickness ～500 μm was formed on the membrane surface (tube side) after 16 h treatment. The oxygen permeation measurement was performed by sweeping the tube side of the membrane with helium to carry away the permeated oxygen. The H2-treated membrane exhibited a large increase in oxygen permeation flux (by a factor of 4.5 at 950°C and 10.5 at 800°C) and a significant reduction in the apparent activation energy, which is attributed to the increased porosity on the tube-side surface. It is suggested that the H2 treatment altered the rate-limiting step from the surface oxygen exchange to the transport of oxygen in the bulk of the membrane. The H2 treatment also led to an enhanced depletion of Ga from the membrane surface, which could affect the applicability of the membrane.