Stability of sulfate doped SrCoO3−δ MIEC membrane

Abstract

A sulfate doped SrCoO3−δ (SC) mixed ionic-electronic conducting (MIEC) oxide, SrCo0.97S0.03O3−δ (SCS), was prepared to study the dependence of its stability on the incorporation of sulfate group into perovskite lattice. The high-temperature cubic perovskite phase can be stabilized down to room temperature by replacing 3% of cobalt-sites with sulfur. However, permeation experiments show that oxygen permeation fluxes through SC and SCS membranes experienced similar degradation processes at 850°C. Hysteresis loops of oxygen permeation fluxes appear on the both membranes indicate a phase transition from cubic to hexagonal during cooling/heating circle of oxygen permeation tests. The results of permeation experiments, annealing treatments in an air or helium atmosphere and the EDS analysis show that more SrSO4 particles are enriched on the sweep side surface. A mechanism analysis on the sulfate group migration from the membrane bulk to surfaces was proposed to help understanding the experimental results. It is concluded that the sulfate group can migrate outside of perovskite lattice and reach to the gas–solid interfaces, so the stabilization function of sulfate to the cubic perovskite phase loses easily as the sulfate doped perovskite membrane encountering annealing treatments or oxygen partial pressure gradients.