In situ formation of a melt-solid interface towards stable oxygen reduction in protonic ceramic fuel cells

Protonic ceramic fuel cells (PCFCs) are one of the promising routes to generate power efficiently from various fuels at economically viable temperatures (500–700°C) due to the use of fast proton conducting oxides as electrolytes. However, the power density and durability of the PCFCs are still limited by their cathodes made from solid metal oxides, which are challenging to address the sluggish oxygen reduction reaction and susceptibility to CO ₂ simultaneously. Here, we report an alternative approach to address this challenge by developing a new melt-solid interface through the in situ alkali metal surface segregation and consecutive eutectic formation at perovskite oxide surface at PCFC operating temperatures. This new approach in cathode engineering is successfully demonstrated over a lithium and sodium co-doped BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3-δ perovskite as the model material. Our experimental results unveil that the unique in situ formed melt-solid surface stabilises the catalytically active phase in bulk and promotes catalytically active sites at surface. Our novel engineered melt-solid interface enhanced the stability of the cathode against poisoning in 10% CO ₂ by a factor of 1.5 in a symmetrical cell configuration and by a factor of more than two in PCFC single cells.