High-performance SrNb_0.1Co_0.9-xFe_xO _3-δ perovskite cathodes for low-temperature solid oxide fuel cells

Chemical to electrical energy conversion using a solid oxide fuel cell (SOFC) becomes more practical as the operating temperature is lowered to 600 °C and below. Given the thermally activated nature of the oxygen reduction reaction (ORR) at the cathode side, development of cathode catalysts with very low polarisation resistance is essential. Here, we showed that partial substitution of Co within SrNb_0.1Co_0.9O _3-δ by Fe (up to 0.5) triggers the formation of oxygen non-stoichiometry while preserving the primitive cubic lattice, thus substantially enhancing the ORR performance below 600 °C (relative to the parent compound). Close correlation between the oxygen non-stoichiometry and ORR activity trends was found to some extent. SrNb_0.1Co _0.7Fe_0.2O_3-δ (SNCF0.2) cathode exhibits a very low area specific resistance value of 0.052 Ω cm² at 600 °C which translates to superior fuel cell performance, e.g. peak power density of 1587 mW cm^-2 at 600 °C. Moreover, the synergistic relationship between ORR activity, thermal expansion coefficient and enhanced CO₂ resistance attests to the significance of the SNCF cathode. The last attribute is envisioned as a dominant factor for applications using alternative fuels (e.g. CO which normally contains CO₂) and in a portable single-chamber SOFC.