Surface modification of La0.3Sr0.7CoO3−δ ceramic membranes

The dependence of oxygen permeability of dense La0.3Sr0.7CoO3−δ ceramics on membrane thickness indicates significant surface exchange limitations to the permeation fluxes, which suggests a possibility to increase membrane performance by surface activation. The cobaltite membranes with various porous layers applied onto the permeate-side surface were tested at 850–1120 K. Silver-modified La0.3Sr0.7CoO3−δ membranes showed enhanced permeation at temperatures above 950 K; deposition of porous layers of PrOx and Pr0.7Sr0.3CoO3−δ had no positive effect. The maximum oxygen permeability at 850–1120 K was observed in the case of porous La0.3Sr0.7CoO3−δ layers with surface density about 10 mg cm−2. These results suggest that the surface exchange of lanthanum–strontium cobaltite membranes under an oxygen chemical potential gradient is limited by both oxygen sorption at the surface and ion diffusion through the surface oxide layers. Oxygen permeability of La0.3Sr0.7CoO3−δ ceramics was found to increase with increasing grain size due to decreasing grain-boundary resistance to ionic transport.