Oxygen Exchange and Transport in (La_0.6Sr_0.4)_0.98FeO_3-d– Ce_0.9Gd_0.1O_1.95Dual-Phase Composites

Abstract

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Oxygen transport properties of tubular Ce0.9Gd0.1O1.95-La0.6Sr0.4FeO3−d composite asymmetric oxygen permeation membranes supported on magnesium oxide

“…The p-type conductivity decreased with increasing temperature in the range 700 °C -900 °C. The same was reported for pure LSF [10] and CGO-LSF [30] composites, where the conductivity increased until ca. 500 °C, went through a broad maximum at temperatures between 500 °C and 600 °C and then decreased with increased temperature above 600 °C.…”

“…A two-dimensional solution of the diffusion problem was used because the conductivity was measured over a short distance close to the center of the sample. For the studied composite additional assumptions were taken: i) the phases are randomly distributed and the composite was treated as an effective medium, ii) at high pO 2 the conductivity change after a pO 2 step reflects only a change of oxygen concentration in the LSF, and iii) at high pO 2 surface exchange occurs only on the LSF surface [30].…”

Surface recrystallization – an underestimated phenomenon affecting oxygen exchange activity

“…The values are found to be in good agreement with values previously reported in the literature (also included in the plots). [2][3][4]26,52 The electrical conductivity of both LSC and LSF decreased with increasing temperature and decreasing pO 2 in the experimental range of this work. The electrical conductivity of LSF was roughly 10 times lower than for LSC and showed a maximum value of 250 S/cm at 500°C.…”

“…24 A fruitful approach to fabrication commercially relevant electrodes with rapid ORR/OER kinetics has been to manufacture composites where perovskites are combined with fast ionic conductors like Gd-doped ceria or even zirconia. 5,[25][26][27][28][29][30][31] In such an approach, one utilizes the best properties of the constituting materials -the fluorite serves as the primary path for oxygen ions, while the perovskite provides catalytic activity for oxygen exchange and a path for electrons. Sometimes, besides providing their separate functions for charge transport more elaborate forms of synergy between the two materials have been reported, where a beneficial effect on one material emerges only when the other one is present.…”

“…Similarly, in a recent paper by Ovtar et al, a five-fold improvement in surface reaction kinetics at 750°C in comparison to pure (La 0.6 Sr 0.4 ) 0.98 FeO 3-δ has been ascribed to the increased amount of Ce 0.9 Gd 0.1 O 1.95 in the composite. 26 Finally, a very promising route for enhancing ORR/OER kinetics of this class of perovskite materials is via surface modification. [32][33][34][35][36][37][38] This strategy includes "infiltration": a method where a small amount of an infiltrating agent (typically nitrate precursors with the desired cations) is deposited onto the perovskite surface and after a thermal treatment forms a nanoparticulate surface decoration increasing the catalytic activity.…”