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L1.04 - Strontium Influence on the Oxygen Electrocatalysis of Highly Oriented La2-xSrxNiO4±δ (0 ≤ XSr ≤ 1.0) Thin Films at Elevated Temperatures 
April 22, 2014   9:30am - 9:45am

Perovskites (ABO3) with high electronic and ionic conductivity and catalytic characteristics1 have been studied intensively for solid oxide fuel cells (SOFCs)2 and oxygen permeation membranes3 at high temperatures. A major barrier that limits the efficiency of SOFCs and oxygen permeation flux is the slow kinetics of surface oxygen exchange on the oxide surface. Ruddlesden-Popper (RP) oxides such as La2NiO4+δ (LNO) can lead to higher oxygen ionic conductivity relative to ABO3 perovskites4 and are interesting alternative cathode materials for SOFCs. By substituting of a larger cation such as Sr2+ (1.31 Ã…) for La3+ (1.22 Ã…) in LNO, the structural stresses are released, which leads to decrease in the amount of additional oxygen to stabilize the structure. Consequently, modifying the rock salts layer where the oxygen diffuse results in the reduction of the oxygen diffusion coefficients.5 However, the influence of Sr substitution on the in-plane and out-of-plane surface oxygen exchange kinetics of La2-xSrxNiO4±δ (LSNO) is poorly understood due to difficulties in the growth of single crystals of LSNO with high Sr substitution.In this study, we investigate how Sr substitution can affect the surface oxygen exchange kinetics of LSNO thin films with a wide range of Sr content (xSr = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) grown on (001)cubic-Y2O3-stabilized ZrO2 (YSZ). The structural orientation of the epitaxial LSNO thin films can be modified from the in-plane to the out-of-plane orientation by increasing the Sr content from 0.0 to 1.0. Such a change in the film orientation can be explained by the reduction in the surface energy of the (001)tetra. surface with increasing Sr as revealed from Density function theory (DFT) calculations. Ex situ Auger electron spectroscopy (AES) indicates no formation of secondary phases across the Sr contents. We show the strong dependence of the surface oxygen exchange rate (kq) of LSNO thin films on the Sr substitution, which can be attributed to the structural reorientation and the adsorption energy change of molecular oxygen on La-La bridge sites.References(1) Adler, S. B. Chem. Rev. 2004, 104, 4791.(2) Adler, S. B.; Chen, X. Y.; Wilson, J. R. J. Catal. 2007, 245, 91.(3) Hashim, S. M.; Mohamed, A. R.; Bhatia, S. Adv. Colloid Interface Sci. 2010, 160, 88.(4) Amow, G.; Skinner, S. J. J. Solid State Electrochem. 2006, 10, 538.(5) Skinner, S. J.; Kilner, J. A. Ionics 1999, 5, 171.

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