Solid oxide cells often employ a diffusion barrier layer, such as rare-earth doped ceria, to mitigate the chemical reaction occurring between common air-electrode materials such as lanthanum strontium cobalt ferrite (LSCF) and state-of-the-art yttria-stabilized zirconia (YSZ) electrolytes. In conventional cell fabrication methods, screen-printed gadolinia-doped ceria (GDC) is often co-sintered with YSZ at high temperatures typically exceeding 1300 °C, which inevitably results in the formation of an interdiffusion layer (IDL) at the GDC/YSZ heterointerfaces. This IDL has been identified as a ceria-zirconia solid solution which has significantly lower conductivity compared to either GDC or YSZ [1]. However, whilst it is commonly acknowledged that such interdiffusion may affect the overall cell properties, there is still a lack of understanding of its actual influence on oxide ion transport and cell degradation behavior.

In this study, we probed the effect of the IDL on oxide ion transport across GDC/YSZ heterointerfaces under fuel cell operation using the 18O oxygen isotope exchange method in conjunction with high-resolution secondary ion mass spectrometry (SIMS) imaging [2]. Two types of cells were examined: one utilizing porous screen-printed GDC interlayers (with IDL), and another utilizing dense GDC interlayers prepared using pulsed laser deposition (PLD; without IDL). A dramatic drop in the 18O tracer concentration was observed coinciding with the IDL location, thereby confirming that the IDL formed at screen-printed GDC/YSZ heterointerfaces inadvertently acts as a major barrier to oxide ion transport. The disruption of ionic flow is attributed to a possible effect of distribution and mobility of oxygen vacancies as induced by the mutual diffusion of cations across the GDC/YSZ heterointerfaces. On the other hand, using dense GDC interlayers prepared via physical vapor processes such as PLD avoids IDL formation, resulting in a remarkable improvement of ionic flow across the GDC/YSZ heterointerfaces. Typical ohmic resistance values for cells with IDL are also found to be higher than those without by approximately a factor of five, indicating that the cell’s increased ohmic resistance can be accounted for by the nature of the GDC interlayer and its associated interfacial properties. Accordingly, the effective mitigation of the IDL formation through an appropriate selection of cell fabrication parameters, specifically those employed for GDC interlayers, is considered as a good strategy towards further improving the performance of solid oxide cells.