Imaging of Oxide Ionic Diffusion at Cathode/Interlayer/Electrolyte Interfaces in Solid Oxide Fuel Cells: Effects of Long-Term Operation

The effects of long-term operation on the oxygen reduction reaction were visualized at the cathode/interlayer/electrolyte interface in Solid Oxide Fuel Cells (SOFCs) by using a stable isotope oxygen ( 18 O) labeling technique with Secondary Ion Mass Spectrometry (SIMS). Real flat-tube stacks were exposed to 18 O 2 before and after long-term operation time (800 hours) for "direct observation" of oxygen/oxide ion motions. The trace of oxygen motions were labeled under fuel cell operation conditions (current density of 0.25 A/cm 2 at 650°C). The SIMS images were taken during electronic shower by E-gun to avoid the charge-up during the measurements. The 18 O incorporation and 18 O 2− diffusion were visualized in a "frozen state" by this technique. High signal counts of 18 O − were obtained at the CeO 2 -interlayer/electrolyte interface, whereas higher 18 O − signal counts were observed inside the CeO 2 -interlayer at the initial condition. A slow diffusion layer of 18 O 2− can be formed after long-term operation and it affects the distribution of high 18 O − signal areas at the interfaces.