  Hydrogen is an important building block in global strategies towards a future
green energy system. To make this transition possible, intense scientific
efforts are needed, also in the field of materials science. Two-dimensional
crystals, such as hexagonal boron nitride (hBN), are very promising in this
regard, as it was demonstrated that micrometer-sized exfoliated flakes are
excellent barriers to molecular hydrogen. However, it remains an open question
whether large-area layers fabricated by industrially relevant methods preserve
such promising properties. In this work we show that electron beam-induced
splitting of water creates hBN bubbles that effectively store molecular
hydrogen for weeks and under extreme mechanical deformation. We demonstrate
that epitaxial hBN allows direct visualization and monitoring of the process of
hydrogen generation by radiolysis of interfacial water. Our findings show that
hBN is not only a potential candidate for hydrogen storage, but also holds
promise for the development of unconventional hydrogen production schemes.
