Investigation of Sc doped Sr₂Fe_1.5Mo_0.5O₆ as a cathode material for intermediate temperature solid oxide fuel cells

In this work we show that the performance of a Sr₂Fe_1.5Mo_0.5O₆cathode can be improved by scandium substitutional doping. Herein Sr₂Fe_1.5-xSc_xMo_0.5O₆(SFSc_xM) compounds are synthesized with a doping value (x) varying from 0 to 0.2, using a glycine-nitrate combustion progress. The phase structure and morphology are characterized by X-ray powder diffraction and scanning electron microscopy showing a perovskite structure and a porous microstructure when doping between 0 and 0.1. X-ray photoelectron spectroscopy results indicate that the Sc-doping has a clear effect on Fe²⁺/Fe³⁺and Mo⁶⁺/Mo⁵⁺ratios. On cells consisting of SFSc_xM electrodes and La_0.8Sr_0.2Ga_0.8Mg_0.2O₃electrolytes, Sc doping is found to be very effective in reducing the interfacial polarization resistance. Impedance data analysis of SFSc_0.05M cathode at a variety of oxygen partial pressures indicates that the rate limiting steps are the dissociation of adsorbed molecular oxygen for the high-frequency arc and the migration of oxygen ions to the triple phase boundary for the low-frequency arc, respectively. The highest single cell peak power density is obtained with the SFSc_0.05M cathode reaching 1.23 W cm⁻²at 800 °C. The results suggest that Sc-doping of SFSc_xM can substantially improve the electrochemical performance.