Enhancing Oxygen Reduction Reaction Activity and CO 2 Tolerance of Cathode for Low-Temperature Solid Oxide Fuel Cells by in Situ Formation of Carbonates.

Development of low-cost and cobalt-free efficient cathode materials for oxygen reduction reaction (ORR) remains one of the paramount motivations for material researchers at low temperature (< 650 ᵒC). In particular, iron-based perovskite oxides show promise as electrocatalysts for ORR because Fe metal is cheaper and naturally abundant, exhibit matched thermal expansion with contacting components such as electrolyte and show high tolerance in CO2 containing atmosphere. Herein, we demonstrated a new mechanism, the in-situ formation of alkali metal carbonates at cathode surface. This new mechanism leads to an efficient and robust cobalt-free electrocatalyst (Sr0.95A0.05Fe0.8Nb0.1Ta0.1O3-, SAFNT5, A= Li, Na, K) for the application of low temperature solid oxide fuel cell (LT-SOFC). Our results revealed that the formation of Li\K carbonates boost the ORR activity with an area specific resistance (ASR) as low as 0.12 and 0.18 Ω cm2 at 600 ᵒC, respectively, which are the highest performance of cobalt-free single-phase cathode that have been ever reported by far. We also find that the chemical stability and tolerance of tested cathodes towards CO2 poisoning significantly improved with alkali carbonates, as compared to the pristine SrFe0.8Nb0.1Ta0.1O3- (SFNT) at 600 ᵒC. This work demonstrates the conclusive role of alkali carbonates to develop highly efficient and stable cobalt-free cathodes for LT-SOFCs and CO2 neutralization.