Ambient-stable storage of molecular hydrogen in crystalline silicon clathrate

Silicon clathrates are crystalline, cage-like silicon allotropes with potential for unique optoelectronic applications. Here, we report a novel discovery in solid-state hydrogen storage using low-sodium type II silicon clathrate films that retain molecular hydrogen under ambient temperature and pressure. Hydrogen was introduced via deuterium plasma at moderate temperatures, forming D2 molecules within clathrate cages. The structure remains essentially intact, with minimal conversion to diamond-cubic silicon after incorporation and thermal release. Supporting evidence shows that only a small fraction of the incorporated deuterium forms SiD or NaD bonds, while the majority remains as molecular D2. Thermal desorption measurements indicate that most deuterium is released below 200 °C. This work introduces a fundamentally new storage mechanism based on molecular encapsulation rather than surface binding or chemisorption. Our findings establish silicon clathrates as the first known solid-state silicon-based material to stably store molecular hydrogen at ambient conditions and point the way toward capacity enhancement.