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The dual-phase membrane has received much attention as the solution to the instability of the oxygen permeation membrane. It has been reported that the oxygen flux of the dual-phase membrane is greatly enhanced by the active coating layer. However, there has been little discussion about the enhancement mechanism by surface coating in the dual-phase membrane. This study investigates the oxygen flux of the CeGdO-LaSrMnO (GDC 80 vol %/LSM 20 vol %) composite membrane depending on the oxygen partial pressure (P) to elucidate the mechanism of enhanced oxygen flux by the surface modification in the fluorite-rich phase dual-phase membrane. The oxygen permeation resistances were obtained from the oxygen flux as a function of P using the oxygen permeation model. The surface exchange coefficient (k) and the bulk diffusion coefficient (D) were calculated from these resistances. According to the calculated k and D values, we concluded that the active coating layer (LaSrCoO) significantly increased the k value of the membrane. Furthermore, the surface exchange reaction on the permeate side was more sluggish than that at the feed side under operating conditions (feed: 0.21 atm/permeate side: 4.7 × 10 atm). Therefore, the enhancement of the oxygen surface exchange kinetics at the permeate side is more important in improving the oxygen permeation flux of the thin film-based fluorite-rich dual-phase membrane. These results provide new insight about the function of the surface coating to enhance the oxygen permeation flux of the dual-phase membrane.

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