Stability of La-Sr-Co-Fe oxide-carbonate dual-phase membranes for carbon dioxide separation at high temperatures

Dual-phase membranes consisting of a mixed ionic-electronic conducting ceramic phase and an ionically conductive molten carbonate phase have the ability to selectively separate CO₂ at high temperature with or without the presence of O₂. This study examines the stability of a dual-phase ceramic-carbonate membrane consisting of La_0.6Sr _0.4Co_0.8Fe_0.2O_3-δ (LSCF) and an eutectic molten carbonate phase composed of Li₂CO₃, Na₂CO₃, and K₂CO₃. LSCF-carbonate membranes exposed to a CO₂/N₂ gradient at temperatures between 800 and 900 C result in a drastic decrease in CO₂ permeation before reaching steady-state after more than 60 h of exposure to the permeating gases due to a surface reaction between CO₂ and the LSCF ceramic phase of the membrane, resulting in decomposition of the membrane surface. The introduction of O₂ in the feed gas, however, helps maintain the LSCF ceramic phase structure and results in stable CO₂ permeation flux at a much higher value due to a change in transport mechanism in the membrane. The results suggest that it is critical to find oxygen ionic or mixed-conducting ceramic materials that are stable in CO₂ environments in order to ensure stability of the membrane for CO₂ permeation.