The H2 seems to be adsorbed by the Si.( That’s why the bubbling in water) It is not a chemical bond. It seems more like a hydrate. We have plenty of natural gas in hydrate form on either coast at great water depths. Yes, it is “nasty” fossil gas. /s.
Metal hydrides have been a safe way of storing and transporting hydrogen, problem is, metal is heavy. This is pretty cool.