Solid-State Catalytic Hydrogen Sponge Effects in BaInO_2.5 Epitaxial Films

Gas sponges capable of absorbing, storing, and releasing ions in a reversible manner are in high demand for advanced electronics, energy devices, and sensors. Here, it is shown that brownmillerite BaInO_2.5 epitaxial films exhibit the capability to act as solid-state catalytic hydrogen sponges at a remarkably low temperature (≈100 °C). Compared to sintered pellets with random crystallographic orientations and many defects, BaInO_2.5 epitaxial films give three orders of magnitude higher conductivity of hydrogen ions, which can be linked to the presence of well-ordered 1D channels and lack of grain boundaries and other defects. Using scanning transmission electron microscopy, it is shown that hydrogen ions can be stored near InO₄ tetrahedral layers of brownmillerite without destroying the parent framework. The high performance and reproducibility of the BaInO_2.5 epitaxial films coupled with ultralow power consumption make them ideal candidates for neuromorphic devices and beyond.