Effect of Firing Temperature on LSM-YSZ Composite Cathodes: A Combined Three-Dimensional Microstructure and Impedance Spectroscopy Study

• Published in: Journal of the Electrochemical Society Vol. 159; no. 4; pp. B385 - B393
• Main Authors: Scott Cronin, J., Muangnapoh, Kullachate, Patterson, Zach, Yakal-Kremski, Kyle J., Dravid, Vinayak P., Barnett, Scott A.
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society, Inc 01.01.2012
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.053204jes

(La0.8Sr0.2)MnO3-Yttria Stabilized Zirconia (LSM-YSZ) cathodes fired at various temperatures were studied using Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) three-dimensional (3D) tomography and Electrochemical Impedance Spectroscopy (EIS). The total cathode polarization resistance, measured at 800°C in air, showed a minimum versus firing temperature, Tf, at 1175°C. The EIS showed two dominant responses that were fit well using a two (R-CPE) element equivalent circuit. The higher frequency (104-105 Hz) response, attributed to YSZ grain boundary resistance within the LSM-YSZ composite, decreased with increasing Tf and was explained by grain size increases estimated from the 3D structural data. The main EIS response, attributed to the oxygen reduction process, decreased in characteristic frequency from 500 to 1 Hz as Tf increased, while its magnitude was minimized at 1175°C. An electrochemical model quantitatively predicted the resistance minimum based primarily on a maximum in the density of electrochemically-active three-phase boundaries (TPBs), measured using 3D tomography. The active TPB density maximum resulted from two factors: substantial particle coarsening and densification at high Tf that yielded a low TPB density, and low LSM-particle percolation at low Tf that yielded a low fraction of active TPBs.