Thursday, 5 October 2017: 10:00
National Harbor 7 (Gaylord National Resort and Convention Center)
Commercialization of SOFCs will be advanced by the development of cell materials and components which operate well at lower temperatures. Lower operating temperatures allow the use of inexpensive ferritic stainless steels as interconnect, improve the chemical and mechanical stability of the cells, and increase stack lifetime. However, oxygen reduction reaction (ORR) kinetics at cathode of the cell is slower at lower temperatures, which significantly reduces the maximum power density of the cell. Electrochemical impedance spectroscopy (EIS) measurements on anode supported bilayer electrolyte SOFCs at 600oC with stabilized bismuth oxide based composite cathode indicated that the non-ohmic polarization accounted for half to two-third of the total cell area specific resistance (ASR). In this work, composite cathodes of various compositions, i.e. weight ratio of electron conducting phase (LSM or BRO) to stabilized bismuth oxide, were fabricated and tested on symmetrical cells using EIS. The starting powder was made by solid-state and wet-chemical methods followed by ball milling to achieve different particle size distributions. Reactivity of stabilized bismuth oxide and electron conducting phase at high temperatures was studied using XRD. EIS spectrum was studied to deconvolute the kinetics of ORR and the performance of the composite cathode as a function of weight ratio and particle size distribution of the two phases was looked at. Lastly, long term performance stability of selected cathode compositions was determined.