Oxygen permeation characteristics of zirconia with surface modification

Abstract

Yttria-stabilized zirconia (YSZ) can be used as an oxygen-permeating membrane at elevated temperature (> 1400 °C) due to its chemical and mechanical stability. It was previously shown that the oxygen transport through YSZ membrane in reducing oxygen partial pressure ( P O 2 ) was highly influenced by the surface-exchange kinetics that can be improved by porous surface coating layers such as YSZ, GDC (Gd-doped ceria) or YSZ–GDC mixture [H.J. Park, G.M. Choi, J. Eur. Ceram. Soc. 25 (2005) 2577]. However, the increased oxygen flux was still lower than that estimated assuming bulk-diffusion limit and rapidly decreased with time due to the sintering of coating layers and the reaction between bulk YSZ and coating layers. In this study, the oxygen fluxes through YSZ with LaCrO 3, GDC + LaCrO 3 (bilayer), LaCrO 3 + 5 wt.% GDC (mixture), or LaCr 0.7Co 0.3O 3 coatings were measured under controlled P O 2 gradient (permeate-side P O 2 : ∼ 3 × 10 − 12 atm, feed-side P O 2 : 2 × 10 − 10 –2 × 10 − 8 atm) at 1600 °C. The oxygen flux drastically increased with these coatings. The highest increase in oxygen flux was shown with GDC + LaCrO 3 (bilayer) coating and was maintained for a long time. The presence of highly catalytic Ce ions while maintaining porous structure in the coating layer may explain the observation. The prevention of formation of resistive layer due to ceria coating may also be partly responsible for the observation.