Abstract
Simple perovskite-structured proton conductors encounter significant challenges to simultaneously achieving excellent chemical stability and proton conductivity that are desirable for many important applications in energy conversion and storage. This work demonstrates that Y-doped complex-perovskite-structured Ba3Ca1.18Nb1.82–xYxO9−δ materials possess both improved proton conductivity and exceptional chemical stability. Neutron powder diffraction refinement revealed a Fm3̅m perovskite-structure and increased oxygen vacancy concentration due to the Y doping. High-resolution TEM analysis confirmed the perturbation of the B site cation ordering in the structure for the Ba3Ca1.18Nb1.82–xYxO9−δ materials. Such combined effects led to improved proton conductivity with a value of 5.3 × 10–3 S cm–1 at 600 °C for Ba3Ca1.18Nb1.52Y0.3O9−δ (BCNY0.3), a value 2.4 times higher compared with that of the undoped Ba3Ca1.18Nb1.82O9−δ. The Ba3Ca1.18Nb1.82–xYxO9−δ materials showed remarkable chemical stability toward water and demonstrated no observable reactions to CO2 exposure. Ionic transport number studies showed that BCNY0.3 had predominantly proton conduction below 600 °C. Solid oxide fuel cells using BCNY0.3 as an electrolyte demonstrated cell power output of 103 mW cm–2 at 750 °C. These results suggest that a doping strategy that tailors the cation ordering in complex perovskites provides a new direction in the search for novel proton conducting ceramics.
