Direct evidence for solid-like hydrogen in a nanoporous carbon hydrogen storage material at supercritical temperatures

Here we report direct physical evidence that confinement of molecular hydrogen (H2) in an optimized nanoporous carbon results in accumulation of hydrogen with characteristics commensurate with solid H2 at temperatures up to 67 K above the liquid-vapour critical temperature of bulk H2. This extreme densification is attributed to confinement of H2 molecules in the optimally-sized micropores, and occurs at pressures as low as 0.02 MPa. The quantities of contained, solid-like H2 increased with pressure and were directly evaluated using in-situ inelastic neutron scattering and confirmed by analysis of gas sorption isotherms. The demonstration of the existence of solid-like hydrogen challenges the existing assumption that supercritical hydrogen confined in nanopores has an upper limit of liquid H2 density. Thus, this insight offers opportunities for the development of more accurate models for the evaluation and design of nanoporous materials for high capacity adsorptive hydrogen storage.