Discovery of the rate limiting step in solid oxide fuel cells by LEIS

The outermost surface of the yttria stabilised zirconia (YSZ) electrolyte in the solid oxide fuel cell (SOFC) plays a dominant role in the performance of the cell. Low energy ion scattering is the only technique, which is capable of studying exactly that surface. Instead of Y2O3, impurities segregated to the outermost surface until it was completely covered by them. This strong impurity segregation was proven characteristic for any YSZ sample. The performance of the SOFC will therefore be completely determined by these impurities. Y2O3 did segregate to the subsurface layer and a difference in interfacial free energies between Y2O3 and ZrO2 of 21±3 kJ/mol was determined. So what normally is explained as surface segregation is in fact subsurface segregation, which also explains the higher Y2O3 concentration measured in this study compared to literature.