One stone, two birds: an impregnated net-like layer boosts oxygen reduction activity by removing and transforming surface segregation.

Alkaline-earth segregation and low electronic conductivity restrict the practical applications of high-performance cathodes in solid oxide fuel cells (SOFCs) and protonic ceramic fuel cells (PCFCs). To address these issues, a unique electrode structure with a sintered active backbone coated with an in situ-formed porous net-like PrCoO (PCO) layer is developed. The effectiveness of this strategy is demonstrated using BaSrCoFeO (BSCF), known for unprecedented oxygen reduction activity but with a great tendency to cause segregation and low electrical conductivity. This design leverages the beneficial characteristics of BSCF and PCO: the BSCF backbone provides high oxygen reduction activity, while the porous net-like PCO layer generated in situ offers high electrical conductivity. More importantly, this approach has the ability to eliminate potential surface segregation and even utilize the segregation by element interdiffusion to form a coating layer with high oxygen reduction activity. Therefore, the PCO-coated BSCF cathode (BSCF-PCO) offers impressive cell performance with a low area-specific polarization resistance of 0.02 Ω cm at 600 °C using a symmetric cell and a maximum power density of 1835 mW cm at 600 °C using an anode-supported fuel cell, which are superior to the cells with the state-of-the-art BSCF (i.e., 0.04 Ω cm and 987 mW cm). Furthermore, this strategy significantly boosts the activity of other cathode materials such as BaSrFeZnO, a typical cathode for PCFCs. This study thus provides a facile, universal in situ strategy for constructing high-performance cathodes by removing and transforming surface segregation for SOFCs and PCFCs.