On the role of ultra-thin oxide cathode synthesis on the functionality of micro-solid oxide fuel cells: Structure, stress engineering and in situ observation of fuel cell membranes during operation

Microstructure and stresses in dense La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) ultra-thin films have been investigated to increase the physical thickness of crack-free cathodes and active area of thermo-mechanically robust micro-solid oxide fuel cell (mu SOFC) membranes. Processing protocols employ low deposition rates to create a highly granular nanocrystalline microstructure in LSCF thin films and high substrate temperatures to produce linear temperature-dependent stress evolution that is dominated by compressive stresses in mu SOFC membranes. Insight and trade-off on the synthesis are revealed by probing microstructure evolution and electrical conductivity in LSCF thin films, in addition to in situ monitoring of membrane deformation while measuring mu SOFC performance at varying temperatures. From these studies, we were able to successfully fabricate failure-resistant square mu SOFC (LSCF/YSZ/Pt) membranes with width of 250 mu m and crack-free cathodes with thickness of similar to 70 nm. Peak power density of similar to 120 mW cm(-2) and open circuit voltage of similar to 0.6V at 560 degrees C were achieved on a mu SOFC array chip containing ten such membranes. Mechanisms affecting fuel cell performance are discussed. Our results provide fundamental insight to pathways of microstructure and stress engineering of ultra-thin, dense oxide cathodes and mu SOFC membranes. (C) 2010 Elsevier B.V. All rights reserved.