Stabilisation of metastable crystalline H2 phase in H2 storage materials

As an energy-dense, potentially sustainable energy vector1, as well as a potential room-temperature superconductor (RTSC)2, condensed phases of hydrogen will play a major role in the future of our energy systems. However, a fundamental limitation to the study and application of dense, solid phases of molecular hydrogen (H2) is that they generally only form at exceedingly low temperatures or extremely high pressures. Confinement of H2 in nanoscale pores of carbon nanomaterials, however, has enabled formation of solid-like H2 at atmospheric pressure at temperatures above the critical point3–5. To understand the potential of nanoconfinement for manipulation of the hydrogen phase diagram, examination of the solids that form inside nanoscale pores and why is needed.
Here we combine both neutron diffraction and inelastic neutron scattering to study of both the structure and rotational dynamics of H2 confined in microporous and mesoporous activated carbons. We reveal for the first time the unique molecular arrangement and distribution of H2 molecules inside the porous frameworks, the explicit crystalline phases that are produced and how nanoconfinement causes the thermal stabilisation of the metastable crystalline phases of H2.
The results of this study indicate how the thermal stability of solid phases of H2 could be increased with further material design, how liquid H2 boil off could be reduced in lightweight storage systems and how other interesting non-equilibrium condensed phases of hydrogen could be achieved.