Evaluation of the relationship between cathode microstructure and electrochemical behavior for SOFCs

The need for high efficiency and low emissions power sources has created significant interest in fuel cells. Solid oxide fuel cells (SOFCs) are desirable for their fuel versatility. Because high-temperature sintering is required for SOFCs, bulk and interfacial microstructural changes may occur in the cathode during fabrication. These changes influence device performance by affecting the various steps of the cathodic reaction and an increased understanding of this relationship may lead to more efficient SOFCs. Symmetric cells with various microstructures were formed using anneals at temperatures ranging from 1150 to 1325 degrees C for 1 h. Dual beam SEM/FIB (focused ion beam) was used to perform 3-D analysis of the microstructure. Microstructural features of emphasis include the triple phase boundary length (L-TPB) and pore surface area. The results were compared with an AC impedance spectroscopy study focusing on charge transfer resistance and oxygen adsorption, A direct relationship between microstructural parameters from an actual cathode and the polarization resistance of the significant elementary steps of the cathodic reaction is established directly from experiment. It is found that both the charge transfer polarization resistance and the adsorption polarization resistance display a power law relationship with L-TPB and pore surface area, respectively. (C) 2008 Elsevier B.V. All rights reserved.