A photoelectron study of BSCF and LSCF perovskites after long term aging at high temperatures and permeation tests
Patrizia Rosa1, Federico Cernuschi2 and Cristina Lenardi1
1.CIMAINA, Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy
2.RSE, Ricerca Sistema Energetico, via Rubattino 54, 20134 Milano, Italy
Among the materials developed as membranes for high temperature oxygen separation (for oxycombustion or coal gasification processes) the nonstoichiometric perovskitic compounds (ABO3−δ) are very promising due to their high permeation. The Barium (BSCF) and Lanthanum (LSCF) strontium cobalt–ferrite are among the most studied mixed ionic electronic conducting materials having interesting properties as Oxygen Transport Membranes (OTM).  Among the two mentioned material families the best compositions results to be La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF5582), which show remarkable permeation properties and adequate structural stability during heating/cooling between ambient and operating temperatures (800◦C<T<950◦C). 
In BSCF samples, the main features of Co 2p and Ba 3d are compatible with both elements in the perovskite phase. After thermal treatment the formation of Co oxides comes out together with the formation barium carbonate and strontium carbonate. This result is compliant with a kinetic decomposition of BSCF membranes, assessing a possible decline in long term permeation performances.
The LSCF membranes do not show any significant change electronic structure compared to the as delivered material. The main achievement obtained by XPS measurements is the accumulation of oxygen ions on both sides. This feature is more evident on the side exposed to the gas flow and is completely removed by the sputtering process. A similar superficial accumulation of oxygen is not evident in the BSCF membrane.
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