In Situ Formation of a Melt-Solid Interface Toward Stable Oxygen Reduction in Protonic Ceramic Fuel Cells

Abstract

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 CO₂ simultaneously. Here, an alternative approach is reported 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 lithium and sodium co-doped BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ perovskite as the model material. These experimental results unveil that the unique in situ formed melt-solid surface stabilizes the catalytically active phase in bulk and promotes catalytically active sites at surface. The novel engineered melt-solid interface enhances the stability of the cathode against poisoning in 10% CO₂ by a factor of 1.5 in a symmetrical cell configuration and by a factor of more than two in PCFC single cells.