Carborane-based metal-organic framework with high methane and hydrogen storage capacities

A Cu-carborane-based metal-organic framework (MOF), NU-135, which contains a quasi-spherical para-carborane moiety, has been synthesized and characterized. NU-135 exhibits a pore volume of 1.02 cm³/g and a gravimetric BET surface area of ca. 2600 m²/g, and thus represents the first highly porous carborane-based MOF. As a consequence of the unique geometry of the carborane unit, NU-135 has a very high volumetric BET surface area of ca. 1900 m²/cm³. CH₄, CO₂, and H₂ adsorption isotherms were measured over a broad range of pressures and temperatures and are in good agreement with computational predictions. The methane storage capacity of NU-135 at 35 bar and 298 K is ca. 187 v _STP/v. At 298 K, the pressure required to achieve a methane storage density comparable to that of a compressed natural gas (CNG) tank pressurized to 212 bar, which is a typical storage pressure, is only 65 bar. The methane working capacity (5-65 bar) is 170 v_STP/v. The volumetric hydrogen storage capacity at 55 bar and 77 K is 49 g/L. These properties are comparable to those of current record holders in the area of methane and hydrogen storage. This initial example lays the groundwork for carborane-based materials with high surface areas.