Microstructure and cathodic performance of La0.9Sr0.1MnO3/yttria-stabilized zirconia composite electrodes

Abstract

Both pure La0.9Sr0.1MnO3 (LSM) and LSM/yttria-stabilized zirconia (YSZ) composite electrode layers were deposited on YSZ electrolyte disks by means of a silk-printing technique, and their cathodic performances were analyzed using impedance spectroscopy and steady-state polarization measurements at 900°C in air. Scanning electron micrographs (SEM) photographs were taken to monitor the microstructural changes which evolved during the course of electrode fabrication and cell operation. In general, the LSM/YSZ composite electrodes out-performed the pure LSM electrode in respect of cathodic activity and electrode long-term stability. The better cathodic activity in composite electrodes likely results from a higher population of three-phase boundary (TPB) sites, whereas the superior long-term stability is due to the suppression of LSM particle growth by the intervening YSZ component. When the cathodic activities of composite electrodes that had been prepared by varying the adhesion temperature from 1000 to 1300°C were compared, that adhered at 1100°C exhibited the best cathodic performance. Interfacial resistance arising from incomplete interparticle contact was the major reason for the cell polarization observed in the electrodes adhered at lower temperatures, while the loss of TPB sites due to particle growth was the main cause for the inferior cathodic activities of those adhered at higher temperatures. 1100°C offers the optimum compromise between two conflicting factors; the interfacial resistance and the TPB site formation. The interfacial resistance caused by the interfacial product layer (La2Zr2O7) turned out to be a minor contribution towards cell polarization.