High Proton Conduction in Ba2LuAlO5 with Highly Oxygen Deficient Layers

Abstract Proton conductors have found diverse applications such as electrolytes of solid oxide fuel cells (SOFCs), but they are required to have high ionic conductivity at low temperatures and chemical stability. Here, we report a new oxide Ba2LuAlO5, which exhibits higher proton conductivity than 10‒2 S cm‒1 between 350 and 800°C, high diffusivity and high chemical stability without any chemical doping. Ba2LuAlO5 is a hexagonal perovskite-related oxide with highly oxygen deficient h' layers, which enables a large amount of water uptake x = 0.22 in Ba2LuAlO5·x H2O. Ab initio molecular dynamics simulations show that the water molecules dissociate into the h' layer and that protons migrate mainly around the interface of cubic closed packed c layers. These results demonstrate that the high proton conduction allowed by the highly oxygen deficient h' and closed packed c layers is a promising strategy for the exploration and development of high-performance proton conductors.