Adjustment of GDC layer microstructure and its influence on the electrochemical properties of microtubular SOFCs

Abstract

The development of a dense chemical reaction blocking layer (CRBL) for micro-tubular solid oxide fuel cells (SOFC) was the aim of this study. The electrochemical performance and stability of SOFCs were also investigated since they strongly depend on fabrication conditions for the electrolyte and CRBL layers. Slurries of two commercial Ce_0.8Gd_0.2O_1.90 powders were prepared and deposited by dip coating onto micro-tubular SOFCs. The results indicate that the layer density and homogeneity are essentially determined by the width of particle size distribution (PSD) apart from the colloidal stability. Two methods were applied for achieving a narrow PSD additional to dispersion: grinding and centrifugation. Particles with a very narrow PSD obtained through centrifugation process could be sintered together even at 1300°C and a layer with a density close to 99% could be reached. In contrast, simple ultrasonic dispersion of powders diminished the distribution width insufficiently and gave porous layer. Impedance measurements showed clear relationship between GDC layer density and ohmic resistance of the cells which directly correlates to their performance with a power density 0.75 W/cm² at 0.7 volt and OCV~1.06 V obtained at 850°C for the cells with the densest GDC layer.