Strong Enhancement of Hydrogen Ion Conductivity in Y-Doped BaZrO3 Films on Al2O3 with the Assistance of Templated Epitaxy.

Hydrogen ion conductors are a key component of solid-state ionics, including artificial intelligence devices, sensors, catalysts, and fuel cells. The interest has been focused on BaZr1-xYxO3 (BZYO, typically x = 0.2) among solid-state hydrogen ion conductors, but high conductivity is only observed in the grain-boundary-free BZYO epitaxial films deposited on impractical cubic substrates. Here, by virtue of a templated epitaxy, we significantly enhance hydrogen ion conductivity of BZYO films by one order of magnitude when we grow the films on industrially practical (0001)Al2O3 with the MgO template layer. X-ray diffraction and transmission electron microscopy reveal that the epitaxy-driven excellent crystallinity of BZYO films allows the suppression of hydrogen-blocking grain boundaries, enabling the facile movement of hydrogen ions. The discovery of fast hydrogen ion conduction in BZYO epitaxial films on Al2O3 will attract great attention for designing inorganic hydrogen ion conductors based on the structure-property relationship and promote economic benefits in hydrogen economy.