Thermal cycling durability improved by doping fluorine to PrBaCo2O5+δ as oxygen reduction reaction electrocatalyst in intermediate-temperature solid oxide fuel cells

Double perovskite PrBaCo2O5+δ (PBC) has received much attention as cathode material for solid oxide fuel cells (SOFCs) due to its excellent catalytic activity for oxygen reduction reaction (ORR), especially at intermediate temperature up to 800 °C. However, its high thermal expansion coefficient (CTE), about twice as the electrolytes, usually results in poor durability. This work presents the effect of CTE reduction by doping fluorine ion to the oxygen-site of PrBaCo2O5+δ. The fluorine doping, which is confirmed with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy investigations, can substantially reduce CTE, from 24.03 × 10−6 K−1 down to 16.78 × 10−6 K−1 as determined with dilatometry while from 26.52 × 10−6 K−1 to 17.46 × 10−6 K−1 with high-temperature XRD. Consequently, the durability is improved by a factor of ∼3.0 when the electrodes are subjected to 200-800 °C thermal cycles. In addition, the fluorine doping does not deteriorate but maintains or even improves the oxygen transport properties and electrochemical performance for ORR of PBC, demonstrating that fluorine doping is very attractive for the development of promising cathode materials for intermediate-temperature SOFCs.