Cobalt doping as a microstructural optimization strategy for Sr₂Fe_1.5Mo_0.5O_6- cathodes in direct ammonia SOFCs for N₂O abatement

Abstract

Perovskite-type oxides are promising materials for mitigating nitrous oxide (N2O) emissions. Although widely studied for thermal N2O decomposition, their application in electrochemical N2O abatement in solid oxide fuel cells (SOFCs) remains largely unexplored. The double perovskite Sr2Fe1.5Mo0.5O6-delta (SFMO) stands out for its mixed ionic-electronic conductivity and redox stability; however, it exhibits low power conversion efficiency when N2O is supplied to the cathode. This work focuses on improving SFMO performance by partially substituing Fe with small amount of Co (Sr2Fe1.5-xCoxMo0.5O6-delta, x = 0.05) to enhance its intrinsic and microstructural properties, aiming to improve cathode performance under N2O conditions in a direct ammonia SOFC (DA-SOFC), operating at 600-750 degrees C. Electrochemical impedance spectroscopy revealed similar reaction mechanisms in both compositions, despite notable microstructural differences caused by Co-doping. The denser SFCMO layers showed better grain connectivity, nearly doubling the peak power density (similar to 30 mW cm(-2)) compared to undoped SFMO, highlighting the beneficial role of microstructural alterations.