Ultra-dense hydrogen in small pore hydridic framework

Abstract Nanoporous materials have attracted great attention for gas storage, however, high volumetric storage capacity remains still a challenge. Here we investigate a magnesium borohydride framework with small pores and a unique partially negatively-charged non-flat interior for hydrogen and nitrogen uptake using neutron powder diffraction, volumetric gas adsorption, and inelastic neutron scattering. Hydrogen and nitrogen occupy distinctly different adsorption sites in the pores with very different limiting capacities: 2.33 H2 and 0.66 N2 per Mg(BH4)2. Molecular hydrogen is packed extremely dense with about twice the density of liquid hydrogen (144 - 132 g H2/L of pore volume), independently measured by three experimental methods. This study reveals that densely packed hydrogen can be stabilized in small-pore materials at ambient pressures.