Oxygen exchange and diffusion in the near surface of pure and modified yttria-stabilised zirconia

By studying the oxygen transport through yttria-stabilised zirconia (YSZ), a strategy could be proposed which should lead to a reduction in the operating temperature of the solid oxide fuel cell (SOFC) to the intermediate temperature range without loss in performance. The combination of isotopic exchange depth profiling with low energy ion scattering (LEIS) and elastic recoil detection analysis (ERDA) has shown a complex structure affecting the surface oxygen exchange reaction and self-diffusion in 10 mol% yttria-doped zirconia. Remarkable is the presence of a thin (about 6 mn) layer at the external surface showing resemblance with the monoclinic phase. The results suggest a significant improvement in the surface oxygen exchange with respect to the values reported in literature when impurity oxides are prevented from segregating to the external surface. A possible operating temperature of around 850 degreesC seems feasible. Improvements in the surface oxygen exchange by addition of a surface catalyst reported in literature are also attributed to the removal of impurities. Further decrease in operating temperature, down to at least 725 degreesC, should be possible by removing the impurities in the bulk, which should lead to a considerable increase in the grain boundary diffusion and by reduction of the electrolyte thickness. (C) 2002 Elsevier Science B.V All rights reserved.