Electrochemical Analysis of Nano-Infiltrated Solid Oxide Fuel Cell Cathodes

Composite solid oxide fuel cell (SOFC) cathodes consisting of ionic conducting scaffolds infiltrated with mixed ionic and electronic conducting (MIEC) nano-particles have exhibited some of the lowest reported polarization resistances in the literature.  In this study, symmetric cell cathodes were prepared via wet infiltration of Sr_0.5Sm_0.5CoO₃ (SSC) nano-particles via a nitrate process into porous Ce_0.9Gd_0.1O_1.95 (GDC) scaffolds to be used as a model system to investigate performance under varying infiltration loadings.  Detailed analysis of the infiltrated cathodes was carried out using electrochemical impedance spectroscopy (EIS).  The results presented show that the infiltrated cathode microstructure has a direct impact on the initial performance of the cell.  Small initial particle sizes and high infiltration loadings (up to 30 vol% SSC) improved initial polarization resistance (R_P).  A simple microstructure-based electrochemical model successfully explained these trends in R_P. Further understanding of electrode performance was gleaned from fitting EIS data gathered under varying temperatures and oxygen partial pressures to equivalent circuit models.  Both RQ and Gerischer impedance elements provided good fits to the main response in the EIS data, which was associated with a combination of oxygen surface exchange and oxygen diffusion in the electrode. A gas diffusion response was also observed at relatively low pO₂.