The overall permeation rate through asymmetric oxygen transport membranes is significantly governed by the porous support. Therefore, the microstructuring of the support's pore structure is essential to achieving the highest performances. Freeze casting is already proven to obtain hierarchical porous structures with low tortuosity, which potentially enhances the oxygen flux of oxygen transport membranes. Although a performance improvement has been reported, such improvement is not self-evident. There has yet to be a detailed comparison of the achieved microstructures in order to identify the relevant microstructural parameters. Asymmetric membranes from Ba0.5Sr0.5(Co0.8Fe0.2)0.97Zr0.03O3- consisting of a surface-activated 20 µm membrane layer with tape-or freeze-cast supports that have identical pore volume and layer thickness were manufactured, characterized, and compared by means of oxygen flux measurements. They were also microstructurally investigated via computed X-Ray tomography and flow simulation experiments. In the air/Ar gradient, the freeze-cast support membrane performs below the tape-cast-supported membrane. In particular, the transition zone close to the membrane, which is caused by the freezing process, significantly constrains the diffusivity and permeability of the support, and therefore leads to concentration polarizations. At temperatures below 800 °C, surface exchange kinetics at the membrane-support interface become rate-limiting.

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The gas flow through porous media including that of multiple species is frequently described by the binary friction model (BFM) considering the binary diffusion, Knudsen diffusion, and viscous flow. Therefore, a numerical simulation was performed on a microporous support of an asymmetric oxygen transport membrane. As its exact numerical solution is complicated and not always possible, the results of two different levels of simplification of the pressure profiles within the porous support are compared to the exact numerical solution. The simplification using a constant pressure equal to the gas pressure outside the support leads to a deviation by up to 0.45 mL·min−1·cm−2 from the exact solution under certain operating condition. A different simplification using a constant pressure averaged between the outside of the support and the support/membrane interface reduces this deviation to zero. Therefore, this is a useful measure to reduce computational efforts when implementing the Binary Friction Model in computational fluid dynamics simulations.