Unveiling the complex interplay between nanoscale electrochemical reactions and microscale electrode architecture in Solid Oxide Fuel Cells via physically-based modeling

Within composite electrodes for solid oxide fuel cells (SOFCs), electrochemical reactions between gas species and charge carriers take place at the so-called three-phase boundary (TPB), which is the contact perimeter among the electron-conducting phase, the ion-conducting phase and the porous phase. The TPB reaction zone is conventionally regarded as a mono-dimensional line and efforts have been made to increase its length to reduce kinetic losses. By using physically-based modeling, 3D tomography and impedance spectroscopy, it is shown here that the electrochemical reactions take place within an extended region around the geometrical TPB line. Such an extended region is in the order of 4 nm in Ni-YSZ anodes [1] while approaches hundreds of nanometers in LSM-YSZ cathodes [2] (Figure 1a). These findings have significant implications for preventing the degradation of nanostructured anodes, which is due to the coarsening of the fractal roughness of Ni nanoparticles [1], as well as for the optimization of composite cathodes, indicating that the adsorption and surface diffusion of oxygen limit the rate of the oxygen reduction reaction (ORR) [2]. Having elucidated the kinetic mechanisms occurring at the nanoscale, guidelines are given to optimize the electrode microstructure via additive manufacturing [3] at the micro and mesoscales by introducing a novel approach for the quantification of inhomogeneous current distribution at the particle level (Figure 1b)