Nanometric roughness of the three-phase boundary in the degradation of infiltrated and redox-cycled anodes

Infiltration of Ni nanoparticles onto ceramic scaffolds allows for a significant reduction of the polarization resistance in SOFC anodes. However, infiltrated anodes undergo rapid degradation within the first few hours of operation. A similar rapid electrochemical degradation affects also conventional Ni-YSZ anodes after redox cycling. Here we show the common origin for these rapid degradations. By combining 3D tomography, impedance spectroscopy and physics-based modeling (Figure 1) we show that Ni nanoparticles, either infiltrated or generated in-situ by redox cycling, create a nanometric roughness at the three-phase boundary (TPB), leading to a high electrochemical activity, which is eventually smoothed/diminished during annealing within 24 h. For the first time, the fractal dimension of the TPB is quantified and related to its lateral extension, being a value of 4 nm. This insight offers the potential to develop new strategies to extend the lifetime of SOFCs.