Comparison of support microstructures for oxygen transport membranes: freeze-drying vs. tape-casting.

Mixed Oxygen Ion Electron Conducting (MIEC) ceramic membranes for separation of oxygen from gas mixtures (OTM) are of great interest for different applications due to their high efficiency and practically infinite selectivity. Existing high performance membranes consist of a 20-50 µm thick membrane layer on a support with random porosity and varying thickness in the range of 500 – 1000 µm. Those membranes possess high oxygen flux, however, a non-adequate support microstructure can become rate limiting for the gas transfer. The gases may accumulate or deplete at the membrane-support interface due to insufficient gas exchange, which leads to a decrease in driving force across the membrane layer itself. Accordingly, microstructural optimization of the porous support architecture is needed, which involves controlled and tailored porosity, tortuosity, morphology, and pore opening diameter. Freeze drying is one opportunity to obtain hierarchical porous structures that potentially enhance the oxygen flux of the membrane.In this work, membranes with different support architectures are fabricated, i.e. hierarchically organized porous supports via water-based freeze drying and its porosity and membrane layer thickness is mimicked by tape casting for direct comparison. The effect of the support microstructure on oxygen flux and mechanical properties has been studied. The results will help to further improve membrane performance and aid the development of mechanical stable thin film membranes