Exploring the capability of mayenite (12CaO·7AlO) as hydrogen storage material.

We utilized nanoporous mayenite (12CaO·7AlO), a cost-effective material, in the hydride state (H) to explore the possibility of its use for hydrogen storage and transportation. Hydrogen desorption occurs by a simple reaction of mayenite with water, and the nanocage structure transforms into a calcium aluminate hydrate. This reaction enables easy desorption of H ions trapped in the structure, which could allow the use of this material in future portable applications. Additionally, this material is 100% recyclable because the cage structure can be recovered by heat treatment after hydrogen desorption. The presence of hydrogen molecules as H ions was confirmed by H-NMR, gas chromatography, and neutron diffraction analyses. We confirmed the hydrogen state stability inside the mayenite cage by the first-principles calculations to understand the adsorption mechanism and storage capacity and to provide a key for the use of mayenite as a portable hydrogen storage material. Further, we succeeded in introducing H directly from OH by a simple process compared with previous studies that used long treatment durations and required careful control of humidity and oxygen gas to form O species before the introduction of H.