(608e) Enhanced Performance of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) Membranes By Atomic Layer Deposition of a Protecting Alumina Nanofilm

The perovskite oxides are promising membrane materials for catalytic membrane reactors for energy and environmental applications as a result of their good oxygen permeation rates mechanical/chemical stability. However, irreversible degradation of perovskite-type membranes occurs under permeation and/or when they are exposed to oxidising gases. Permeation or an oxidising environment can drive segregation of cations and can result in the formation of undesired phases at the perovskite surface.

Here we demonstrate enhanced peformance of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) membranes by growing an alumina (AlO_x) nanofilm on their surfaces using atomic layer deposition (ALD). ALD is known for its high quality and conformal film deposition with atomic-scale uniformity. Alumina nanofilms were prepared on the permeate side of the membrane which was subsequently exposed to an inert stream or a stream containing 200 ppm hydrogen sulphide during permeation experiments. Permeation rates of the bare LSCF membrane and ALD-LSCF membranes with different thickness of alumina film (1 nm to 100 nm) were evaluated at 900^oC. A 30 nm alumina film (30nm-ALD-LSCF) showed a limited sacrifice of oxygen permeation: less than 15% decrease compared to the permeation rate of the bare LSCF membrane before exposure. Furthermore the ALD modification conferred a protective effect on the membrane slowing sulfate formation. After 24 hours of hydrogen sulfide exposure, more than 80% of the original oxygen permeation rate was achieved for the 30nm-ALD-LSCF membrane, while less than 35% of the oxygen permeation rate was obtained for the bare LSCF membrane. Over longer durations of 96 hours the 30nm-ALD-LSCF still exhibited 80% of its original permeation rate. A range of characterisation techniques were employed to study the membrane before and after permeation including cross-sectional high angle annular dark field (HAADF) TEM and EDX. The mechanistic behaviour of the composite membrane will be discussed.