Apparent Oxygen Uphill Diffusion in La0.8Sr0.2MnO3 Thin Films upon Cathodic Polarization.

Tobias M Huber,Gernot Friedbacher,Herbert Hutter,Edvinas Navickas,Jürgen Fleig

doi:10.1002/celc.201500167

Abstract

The impact of cathodic bias on oxygen transport in La0.8Sr0.2MnO3 (LSM) thin films was investigated. Columnar‐grown LSM thin films with different microstructures were deposited by pulsed laser deposition. 18O tracer experiments were performed on thin film microelectrodes with an applied cathodic bias of −300 or −450 mV, and the microelectrodes were subsequently analyzed by time‐of‐flight secondary ion mass spectrometry. The 18O concentration in the cathodically polarized LSM microelectrodes was strongly increased relative to that in the thermally annealed film (without bias). Most remarkable, however, was the appearance of a pronounced 18O fraction maximum in the center of the films. This strongly depended on the applied bias and on the microstructure of the LSM thin layers. The unusual shape of the 18O depth profiles was caused by a combination of Wagner–Hebb‐type stoichiometry polarization of the LSM bulk, fast grain boundary transport and voltage‐induced modification of the oxygen incorporation kinetics,

Highlights

La0.8Sr0.2MnO3 (LSM) and similar perovskite-type materials are widely investigated for solid oxide fuel cell cathode applications.[1]
Columnargrown LSM thin films with different microstructures were deposited by pulsed laser deposition. 18O tracer experiments were performed on thin film microelectrodes with an applied cathodic bias of À300 or À450 mV, and the microelectrodes were subsequently analyzed by time-of-flight secondary ion mass spectrometry
As shown in Ref. [5f] by using atomic force microscopy (AFM) and transmission electron microscopy (TEM), LSM layers deposited at 600 8C have grain diameters of about 30 nm and those deposited at 830 8C consist of grains that are roughly two times larger

Summary

Introduction

La0.8Sr0.2MnO3 (LSM) and similar perovskite-type materials are widely investigated for solid oxide fuel cell cathode applications.[1]. Higher oxygen vacancy concentrations result and can improve the electrochemical performance of LSM electrodes. The bulk path of oxygen reduction may be highly important in thin films and in polarized porous LSM cathodes.[4] Simulations of the relevance of the bulk path in polarized LSM electrodes are presented in Ref. An applied cathodic bias further affects the oxygen incorporation rate at the surface, though details of these changes and of the oxygen incorporation mechanism in LSM are not yet well understood. Additional experiments on LSM electrodes under operating conditions are needed to obtain a clear picture of the kinetics of [+] These authors contributed to this work

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