Enhancing oxygen permeation through hierarchically-structured perovskite membranes elaborated by freeze-casting

Abstract

Innovative asymmetric oxygen-transport membrane architectures were prepared by combining freeze-casting and film deposition techniques. Freeze-casting enabled the optimization of the gas transport through the support by creating a hierarchical porosity while a dense top-layer of 30 μm was coated over this support by screen printing. The versatility of this technique was demonstrated by preparing highly porous bodies made of fast ionic conductors, e.g. perovskites and doped ceria fluorites, with a large number of applications in catalysis, electrochemistry and gas separation. Permeation tests using an all-La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ asymmetric membrane proved the beneficial effect of such porous supports over the O₂ fluxes with a maximum value of 6.8 mL min⁻¹ cm⁻² at 1000 °C, markedly above the results achieved so far with conventional preparation techniques. Gas permeance study through the porous freeze-cast support showed that the particular pore structure allows the gaseous transport resistance to be minimized. The related pressure drop is found to be very low in comparison with conventional porous supports, e.g. tape-cast supports, with for example only 0.59 bar mm⁻¹ with argon at 800 °C for an inlet flow of 400 mL min⁻¹ cm⁻². Finally, the stability of the asymmetric membrane has been evaluated under CO₂ atmosphere during 48 hours and at 900 °C. The membrane is found to be stable without deactivation nor decrease in the O₂ permeation flux.