The migration behavior of sulfur impurity contained in the dual-phase membrane of Ce_0.9Gd_0.1O_2-δ-SrCo_0.8Fe_0.1Nb_0.1O_3-δ under CO₂ atmosphere

In this study, migration mechanism of sulfur impurity contained in dualphase membrane (DPM) of Ce_0.9Gd_0.1O_2-δ-SrCo_0.8Fe_0.1Nb_0.1O_{3 -δ} during oxygen permeation process was systematically investigated. Sulfate phase was observed on the permeate side of the DPM after oxygen permeation using CO₂ as sweep gas. Experimental results indicated that the migration of sulfur was driven by the chemical potential gradient of oxygen and CO₂ sweeping obviously speeded up the migration rate. Theoretical calculations on the SrCoO₃ suggested that Sr atoms tend to shift from subsurface to the surface even the initial surface is fully terminated by Co/O, which is beneficial to the CO₂ adsorption and generates Sr- and O-vacancies. Sulfur atoms favor to occupy O-vacancies in the beginning; however, due to the formation of carbonates associated with CO₂ sweeping, sulfur may hop from the O-vacancies in the bulk to the Sr-vacancies on the surface, forming mixed sulfate and carbonate. In addition, the decrease of sulfur impurity leads to an increase of oxygen permeation flux, about a high and stable flux of 0.30 mL min^-1 cm² was achieved at 900 °C under air/CO₂ gradient.