Elucidation of the Oxygen Surface Kinetics in a Coated Dual-Phase Membrane for Enhancing Oxygen Permeation Flux

Abstract

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.

Toward High Performance Mixed Ionic and Electronic Conducting Perovskite-Based Oxygen Permeable Membranes: An Overview of Strategies and Rationales

“…To simplify the analysis of the oxygen permeation rate, the characteristic thickness L c = D */ k s of the membrane is usually used to analyze the impact of the surface exchange reaction. − When L < L C , the surface exchange reaction becomes the main speed control step of OPM; when L > L C , the speed control step of the diaphragm is mainly bulk diffusion . For example, Li et al mentioned that the characteristic thickness of the BaCe 0.1 Co 0.4 Fe 0.5 O 3‑δ membrane is 0.7 mm.…”

Recent Progress and Challenges in Mixed Ionic–Electronic Conducting Membranes for Oxygen Separation

“…It is the active layer material most commonly used to improve the oxygen permeability of fluorite‐rich dual‐phase membranes. The use of an LSC64 active layer generally improved the permeability of all membranes, [ 14,15,59,66–73 ] and the thinnest membrane (≈30 ), 80 vol% GDC–20 vol% LSCF, [ 14 ] showed the largest increase in permeability. This tendency toward improved oxygen permeability suggests that as the membrane thickness decreases, the surface exchange kinetics becomes dominant.…”

Enhancement of oxygen permeation fluxes of La0.6Sr0.4CoO3− hollow fiber membrane via macrostructure modification and (La0.5Sr0.5)2CoO4+ decoration

“…As a result, surface exchange reaction becomes the rate limiting step for permeation through hollow fiber (Han et al, 2016;Zhang et al, 2015). To enhance the permeation rate further, surface modification approach can be performed such as the surface roughening achievable via acid etching (Yang et al, 2017) or methane activation (Liu et al, 2009) and the deposition of porous metal oxide layer or active noble metal(s) or transition metal(s) on the surface (Han et al, 2015;Zhang et al, 2015;Na et al, 2017). Sase et al previously reported the accidental formation of perovskite oxide/Ruddlesden-Popper oxide heterophase interfaces of La0.6Sr0.4CoO3/(La,Sr)2CoO4 (LSC113/LSC214) at the surface of 1400 o C sintered La0.6Sr0.4CoO3 disk (Sase et al, 2008).…”