Hebb-Wagner polarization assessment of enhanced oxygen permeability for surface modified oxygen transport membranes

Tri-layered “porous | dense | porous” La0.8Sr0.2Cr0.5Fe0.5O3−δ-Zr0.84Y0.16O2−δ (LSCrF-YSZ) oxygen transport membranes (OTMs) were fabricated and permeation resistances from oxygen reduction and evolution reactions were determined by using Hebb-Wagner polarization method after introducing additional electron-blocking YSZ thin layers within the dense LSCrF-YSZ layers. Adding nano-scale catalysts, i.e. La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCoF) on air side and Ce0.8Sm0.2O1.9−δ/Ni (SDC/Ni) on CH4 side, into the porous LSCrF-YSZ layers yielded substantially reduced interfacial polarization resistances, and thereby allowed for high oxygen permeability at reduced temperatures under the air/CH4 gradient, e.g., 1.1 and 4.3 ml cm−2 min−1 at 650 and 800 °C, respectively. Analysis of the impedance spectra suggest that the oxygen reduction kinetics on air side was probably limited by charge transfer reaction at T ≥ 750 °C and surface oxygen exchange at T ≤ 700 °C. Meanwhile, oxygen evolution reactions on CH4 side dominated the total resistances to oxygen permeation through the tri-layered OTMs.