Robust CO₂ and H₂ resistant triple-layered (Ag-YSZ)/YSZ/(La₀.₈Sr₀.₂2MnO₃-δ-YSZ) hollow fiber membranes with short-circuit for oxygen permeation

Abstract

Oxygen selective ceramic membranes have many important applications, not only for air separation but also as membrane reactors for cost-effective chemical synthesis. However, the prerequisite to realize these potentials is their stability in the presence of acid gases of CO2 and reducing atmosphere containing H2 and CH4. This work seeks to validate the applicability of robust triple layer hollow fiber membranes consisting of (Ag+YSZ)/YSZ/La0.8Sr0.2MnO3-δ (LSM)+YSZ to separate O2 from air in the presence of these unavoidable gases for more advanced applications. To prepare the triple layer hollow fiber, the dual-layer fiber was firstly synthesized via a combined phase inversion and sintering method where the dense YSZ layer was present on top of the porous LSM-YSZ layer. We further deposited either porous Ag or its mixture with YSZ layer above the dense YSZ surface. The final fiber consists of three layers in sequence from outside surface to inside surface of Ag+YSZ/YSZ/LSM+YSZ. The dense central YSZ layer acts as the ionic conducting phase to prevent gas diffusion while the other two porous layers serve as the electronic conducting phase with catalytic effect to enhance the surface reaction kinetics. To overcome the electronic conductivity limitation of YSZ, silver (Ag) short circuit paste was additionally used to seal the membrane and electronically connect the outer and inner surfaces for electron shuttle for the two surface O2 exchange reactions. Ag-YSZ coated fiber performed better than Ag coated fiber and showed increasing fluxes from 0.1 to 0.53 mL min−1 cm−2 upon increasing temperature from 700 to 900 °C. The O2 fluxes remained constant irrespective of changing the sweep gas from pure He to its mixtures containing CO2, H2, or CH4; mirroring the membrane robustness to tolerate these gases at high temperatures.