Abstract
Many efforts are being made to tune perovskite thin film cathodes toward improving their oxygen reduction kinetics and thereby improving overall solid oxide fuel cell performance. One approach is to enhance oxygen diffusion via introduction of larger concentrations of grain boundaries during thin film growth. While such grain boundary engineering has been shown to enhance ionic transport and surface reaction kinetics in some cases, little attention has been paid on its corresponding influence on electronic conductivity. To provide insights into the role of grain boundaries and their contribution to the cathode performance, we have investigated separately the electronic and ionic conductivity of La0.8Sr0.2MnO3 (LSM) thin films by Van-der-Pauw and 18O tracer exchange measurements respectively, as well as their combined contributions by electrochemical impedance spectroscopy. All three types of experiments were performed on the same kind of samples with varying LSM microstructure to illustrate the effects of grain boundaries on both electron and ion conduction. Correlations between active electrode area and microstructure-dependent partial conductivities are presented. The findings can also be used for optimizing current collector spacing in thin film solid oxide fuel cells.
Highlights
Interplay of Grain Size Dependent Electronic and Ionic Conductivity in Electrochemical Polarization Studies on Sr-Doped LaMnO3 (LSM) Thin Film Cathodes
All the measured LSM thin films on YSZ exhibit activation energies between 0.09 eV and 0.12 eV in the temperature range from 300◦C to 700◦C
The electronic and ionic conductivities of LSM thin film samples were investigated by Van-der-Pauw measurements and 18O tracer exchange experiments
Summary
Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/. Interplay of Grain Size Dependent Electronic and Ionic Conductivity in Electrochemical Polarization Studies on Sr-Doped LaMnO3 (LSM) Thin Film Cathodes. LSC readily reacts with YSZ and exhibits a large effective thermal expansion mismatch with YSZ leading to the buildup of potentially destructive stresses. It has been demonstrated via 18O/16O oxygen exchange experiments, followed by secondary ion mass spectrometry (SIMS) concentration profile analysis, that grain boundaries in LSM exhibit orders of magnitude higher oxygen diffusivity and oxygen surface exchange. We give experimental examples how a reduced in-plane electronic conductivity due to resistive grain boundaries affects impedance spectroscopic studies of micro-patterned thin film electrodes. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract)
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